It's not a "switch" per-se (though some of the kits have realtime tuning switches to make more/less smoke on demand).
It's a purposely poorly-turned engine + accelerator control.
TL;DR: poor turning, and floor it (high RPM).
This video gives a pretty good overview: https://www.youtube.com/watch?v=miTnnJ7xMv8
Ah, even worse, you can gas people and your engine pollutes normally as well.
I didn't think people would be this shitty, but here we are.