How to cure a dead fingernail?

Does anyone knows how to cure a dead thumb nail? I was riding a cab last week when im about to close the door i didnt notice that my thumb was still at the very edge of the cab door. When I slammed the door i just felt the pain run into my body. I saw my poor dead thumb in the cab door. I think this is the most stupid thing happened to me. How can someone didnt noticed it and just close the door. So so stupid. I was in a hurry that time cause im almost late for work. So please please if someone knew any cure about it or will it just heal naturally???