Body damage how to fix

I have this box with body damage in the back corner. It was in an accident and it looks like the guy ponded the damage out with a punch and a hammer. Anyone have a good idea on how to fix this. I would like to do it with steel but dont know where to start. Maybe pound it back into shape with a block and fiberglass it smooth. Help would be appreciated. thanks.

with body work you will never get it to 100% with just a block and hammer. a little bondo goes a long way