Don’t worry about technique, or gaining strength for your left arm, but try to do a overhead press with very light weights (5-10 lbs) for your left arm to coordinate better.
Stop when you start feeling stress in your left arm, then take a break, and then do more. Keep repeating this, until you feel any tiredness in your left arm.
The goal of this exercise is to do as much overhead press with your left arm in a day, so your left arm can coordinate better.
