How to slow down the yeast depends on how you are adding it to the tank.
If you have it in a heated bucket, turn off the heat. Let it run at room temp. Add back heat to adjust the bubbles.
Use a smaller bottle, a gallon jug can be too much, depending on your water. Or just put less sugar in the mix you use.
Adjust the difuser or reactor to be less efficient. If it is a Hagen/Nutrafin diffuser, move the output to a higher level so the bubble travels on less than the full ramp system. If it is a DIY vortex or gravel tube, take the sponge out of the end to let some bubbles escape. If it is an inline reactor, um, I don't know how you could work it, better just change the mix.
In all of these, it is better to have a bubble counter in the system so you can monitor how things are going.