Super dented right butt cheek due to trauma and undergone surgery. What can be done to fix this problem? (Photo)

It is a little hard to tell from just your photos, but I think you would be a good candidate for fat grafting to the deficient area. You are very thin, but hopefully there is a few small pockets of fat that can be borrowed. If the scar is stuck down to underlying tissues then you may need a scar release also. With difficult scars sometimes it takes more than one grafting procedure to get the best result.

This type of scar can be improved first, by releasing the adhesions to the muscle, and then using a filler. The best filler will be your own fat, but if you are very thing and don't have any fat to spare, Sculptra (injectable poly-L-lactic acid) is a good temporal option.