I pinch until you feel it pop. Others twist the stem, but found myself holding a topless plant doing this. Meh
This slows down the elongation of the stem and increases vascularization, which then increases elongation. So after a few pinches, you have a slightly shorter plant that pulls harder on the roots because of increased capillary capacity. This in turn increases the volume of nutrients delivered to buds beyond the pinches making bigger buds.
Look up Supercropping for more extensive explanations.
I’ll post some post pinch pics in the next update for you.
Thank you for your interest.
-al