Make the dent and surroundings warm with the paint dryer. Note: the paint must not become too hot!
Then spray CO2 on the dent. The outflow temperature of carbon dioxide snow is -50 ° C near the expansion tube.
Apparently the system also works with a compressed air spray can from the photo shop.
If everything goes as it should go, the sheet metal jumps with a clear "KLONK!" back (as good as) back in model.