im doin some lst with this tall fucker, started about 1 week before flower bcos i realised that if it doubled (even tripled!) in hieght during flowering i would have a 12 footer!!! ahaha maybe not but too tall for my backyard none the less..
just pulled it to the side and gona make it extend horizontally as much as possible, let the 'top cola' grow longer vertically then tie it down and so on
this is just how ive done it but there are many ways to keep ur plant low as other ppl have suggested
hope this helps
peace.