The Ready State Virtual Mobility Coach is like having a virtual Kelly Starrett in your pocket.
Scapular winging when putting the hand behind the back is likely not long thoracic nerve damage. With nerve damage the scapula would be winged out at rest. You are probably just super tight in the front of your shoulder. Address it with videos about the anterior pec wall and internal rotation. If you aren’t a member already you can sign up for a 10 day trial.