Some folks drill holes and use a threaded slide hammer then weld up the hole. Some folks weld a washer or stud on. Others use the stud gun to keep it more simple. I use them all but the way you choose to go about it depends on the metal structure, the thickness of the metal, and whether the part can be dismantled for regular hammer and dolly methods. I must have over a hundred different tools that I have fabricated and purchased for metal forming or reforming. I have MIG, TIG, and oxy acetylene to choose for welding. Most of the time I use the O/A torch.
I sometimes have better luck just cutting out the bent part and welding in a new piece.