Depending on the severity, if the dent/curve is small enough, you could try automotive putty assuming you'll be painting it, otherwise, if its not too noticeable, i'd just live with it.
I'm currently repairing my coin door and trying to straighten out damage (from people trying to pry open the door) is taking alot of force with a hammer on a steel workbench - dont like your chances of getting it flat.
Thing to note with metal, the more you work it to get it flat, the more the metal "stretches" causing all kinds or warping issues.
