I do them myself on my Topaii cases.

If you want a proper job then take it to a repairer. If you hammer it out yourself them you'll still see the residual damage plus hammer marks but at last you'll get the shape of the case back.

I used a hammer and hammered from the inside. Be sure to use a towel between the hammer and the dented area so you don't damage the blue internal lining.

I'd say my case(s) have character!