Eruditus

I have extremely limited external rotation in my left shoulder due to an injury at birth to my brachial plexus which has resulted in Erb's Palsy in my left shoulder/arm. One or many of my nerves has been affected by Wallerian degeneration and I truly wish to improve my range of motion as much as humanly possible by activating the connection to the infraspinatus and teres minor muscles. Is this possible? How do I regrow the nerves to these parts of my body, and what exercises, vitamins, diet changes, or anything else will I need to promote recovery?

Also, I cannot supinate my arm palm up due to the lack of external rotation, and my scapula wings fairly easily. My bicep is shorter on my left arm, and weaker. Also, my deltoid contracts when doing a curling motion with my left arm, and my shoulder pops and is sometimes painful.

Sincerely,

David