Cut a v shape in the very top of the plant leaving the two little leaves on each side. I just tried this last week for the first time on one of my clones and slipped oops I cut the top off. Keep a steady hand my Friend a you shall be rewarded. I read a post A few years ago that said the cells are multiplying and growing in every direction at that point on the plant and he reported as many as 8 tops growing at one time. I cant produce this post as evidence for this statement so take it for what it is worth.
Good luck
MCM