m0useanswered grow question 8 months ago Anytime after the 3rd week or 4th-5th node. is a good standard. A plant node is the joint were two leaves grow out of.
Go slow and be gentle, it is stress but its lightly applies vs HST that is high stress like branch snapping and removal.
There are LST clips out there that do this for you, or go to dollar store and get some string, lots of options.
Best to have a vision in mind on how you want to train the plant, going in with out a plan can just lead to poorly trained plants and make a mess. If this is new to you google some articles on hot to LST and get a frame set of whats going on. Read multiple posts to have a better understanding and see other styles. I tend to go in a spiral pattern from the base of the plant aorund the pot/stem.
Good Luck!