I am not a vet
There is not much you can do about the damage. Your concern should be about infection or disease in the open wound. I would go to your local fish store and talk to someone who has been in the business a while about remedies if that happens.
I would treat it with a 3% saline solution for no more than 10 minutes with aireation, this will help reduce the possibility of parasites. If your pond does not have salt in it, I would make it .1% for now. If you have water plants, some may not like it but the fish will.
I run hot and cold on the .1% in my own pond due to water plants. My tanks are all at .1% (I have over 1000 fry in those).