It looks like you have enough room left in the pot to add more soil. I typically bury them up an inch or two at transplant but you can easily just add more soil now.
Move your light down a little bit till you get to about 300 PPFD. You can download a PPFD meter on your phone to test your light output at your plants.
Add more airflow to the plants, they will strengthen up their stem on their own when they experience more movement.
When I do LST early, I use wire and make a little loop on the end of an 8-10” piece. I put the loop over the branch and shove the straight part down into the soil. Works great for early stages of LST.
Hope this helps.