nice find. Not done this with a coin but heard about heating the object up before bending on youtube. did it with a silver spoon recently with soaking it in hot water.
Heat is the key and keep it hot while pressing SLOWLY. Straighten a little, reheat, more straightening, repeat till desired flatness is achieved. I would use leather pieces on either side as to not damage the surface any more than it already is. If this is a fire coin it may be brittle. You do what you feel comfortable with. I'm no expert by any means but I have had to straighten a lot of different types of metal over the years. Good luck and show us how it turns out.