often people try to fix the left leg forward by trying to bring the left leg back. Better to think about doing another action, that is a positive one, than trying to NOT do an action.
For example. If you have your left leg advanced, it might be because you are over weighting your right seat bone. So, try to weight your left seat bone. Also , look and see if one shoulder is advanced over the other, which would also make one leg go ahead of the other. There's some kind of twist in the body that makes the leg go forward. So, you counter it by weighting the part that is being pulled off the saddle by the twist.