Well since you have frozen and snail food options try to switch around foods (I'd start with frozen so he/she doesn't get hooked on live foods first and refuse frozen). With any new food and feeding schedule for the fish it may take a few trys/days before it eats, but it will.
Feeding Schedule: if convenient for you, two very small feedings a day work, but one feeding a day is fine too (feeding frequency can be reduced by keep live snails in the tank to hunt, but be mindful these snails are an added bioload).
Feeding Amount: Sadly I can't give a formula for how many worms to feed... shot in the dark 4-8 black worms per a feeding, depending on size and how eagerly the puffer goes after them (you can keep an eye on how big its stomach gets as it eats). They can survive in warm water so if he/she doesn't eat them they may burrow into the substrate, and get eaten whenever they pop up. Don't have a good quantity guess for frozen food yet.. the 2 puffers here are still not keen on the stuff to know how much they'd eat, sorry. I'm sure you can watch some Youtube videos of others feeding their puffers frozen foods to get a rough idea for amounts.
Live Blackworm Care: if you are starting out with a tbs, you won't be able to feed them to the puffer very often if you want their #s to grow, they will make more but its not fast going. If you want to get more, i bought mine from easternaquatics.com, its in Pa so closer than buying from the Ca source. You can also ask for more care tips via email or phone.
First off, if you do not have it get Seachem Prime: its a de-chlorinator that also binds ammonia and nitrite for 48 hours when used in up to 5x dose. Use this stuff, it keeps the worms from dieing of ammonia toxcity, this lets you keep them in unfiltered containers. For your small amount you have I'd first split the group in half, always good to have a 'back up' culture in case somethign happens. You can keep them in Tupperware/small plastic storage containers (if you already have some make sure its VERY clean no soap/detergent/food left in there.. also don't use it for food again.. your family will not be happy :p), I'm using
But you do not need a container this big, i have large ones since I usually buy about 1/2 lb of worms to last a long while (shipping is $30, so do not want to buy often)
I only fill my container about 1/2-2/3 with water, these worms prefer shallow water as they will climb the walls to get that the surface for air. (worms are hiding its right after a bath, they're under the paper)
For food of the worms all you need a brown paper bag (the less ink print on it the better) or organic brown paper towels (white ones usually contain bleach, that how they got white). I went with paper bags as I can get them for free at the grocery store, just request paper.
Rip off a chunk and stick it in the container of water (this is a mostly used bag).. note I do not put in the glued edges or any parts with ink.
Since you are keeping worms in an un-cycled tank, you will have to change their water and "bath" them often to keep them alive (do not go several days/weeks without bathing.. I did with the first batch.. the smell of rotting worms is worse than an old person's very used diaper...).
How you go about cleaning and how often can be done several different ways. The company i got my worms from said: get a clean milk jug, fill with water and store in fridge for next day use and wash worms with this jug water every day.
Well I tweaked that and lost the jug (cold water tap here is close to what fridge water temp would be). I started with daily washing... but have moved to ever other day since I have very few worms (if you get a large amount or keep them in a very tiny container daily washings are strongly recommended).
Sorry no photos for this part, i need both hands for cleaning (won't want to drop phone in water)
Always wash your hands thoroughly before and after any contact with fish tanks and fish live food cultures (not because 'you'll get a disease', just good hygiene, also black worms are tiny so having leftover whatever on your hands when you wash them can effect them)
Take worms to sink, have a second container 1/4 full of cold tap water.
Remove brown paper towel/bag from bin (check it for worms some stay on.. shake them back into the main container or the cleaning one) and paper set aside somewhere clean (don't want food particles/soap/etc getting on it).
Slowly and carefully tilt the container to drain water from worms bin down the sink (I'd recommend a mesh strainer as you start out its easy to have a worm slip into the sink, don't want to loose any!).
When worms are in a small ball with very little water left over them, dump them into the cleaning container with 1/4 water
Wash out the worm's main bin (the inner plastic may feel slimy inside, get that stuff off)
Refill main bin to desired water level (remember they like shallow water, but don't make it so shallow they are sticking up out of the water when they ball up together).
Focus on cleaning container with worms, swirl your finger around the water by them or gently directly in the worm blob, this will make them separate and give you a chance to easy find any dead ones (dead ones will be extremely pale/white and not move back into the worm ball, though live worms may cling to them).
If you see any dead ones remove them, if not, carefully drain the bin then refill and drain one more time(does not need a lot of water).
When most of the water is removed again pour the worms and the remaining water back into their main container.
Put paper bag/towel back in water over top of them (ah dark place). You will have to change out the paper ever few washes (my paper bag strips last 7-14 days), you'll know when by it becoming slimy and/or breaking down as you try to get it out of the water. Just remove it and give them a fresh piece.
Dose Seachem Prime, calculate how much water you have in the bin and do all that math-y good stuff to figure out how much prime to dose to safely bind ammonia.
Put worms someplace cool and dark for main storage (mine stay in the basement usually doesn't get above 68F, I'm bad about putting them somewhere dark though.. might forget them).
Over time you'll notice very thin tiny new worms, (babies yay!) Be mindful of them when doing the water changes/baths so you don't loose them down the drain, they are very tiny and hard to grab without crushing if they get loose into the sink.
Again this is just how I do it, it is not "the only way" find what works for you.
For feeding the puffer you can just pinch some up with your fingers, use tongs/tweezers, or needless syringe. I feed puffers right after the worm bath and fresh dose of prime, so I'm not introducing ammonia heavy water to the puffer tank (even bound, it will just mean more nitrates after the filter BB is done with it).
Btw the worms are kinda fun to handle out of water, like cold live wiggly angel hair pasta on your fingers, get use to them, don't get grossed out or it'll be harder to care for them.
If you buy blackworms from easternaquatics.. they come with leeches, don't freak out! You can get rid of them easily.. the leeches will cling to the container was you drain water and remove worms, so do a few baths when you first get the worms to remove the leeches (they're tiny things, and not really harmful.. but its a leech.. soo yeh out they go). When the leeches are stuck to the side of the empty container either push them off with a finger or use whatever to get them off, try to throw them in the trash (they're aquatic leeches and will dry out) not down the drain. No photos of leech but they're small kinda ovular with pointed tips at 'head' and 'tail', flat, and very pale/white/peach colored, easy to tell apart from live blackworms. I did not have any issue with leeches latching onto me when removing them.
I do not know if other blackworm supplies will come with leeches or not, I'd think most large worm farms have them.
Hope my rambling offers some helpful info, if you have more questions feel free to ask, or post a thread in the fish section (like "What's your dwarf puffer feeding regime?" or "blackworm live culture care?"). There are several other owners and everyone does things differently, and are happy to share their experiences/knowledge.