If you only have a few dimples and want to do things on the cheap, make yourself a sand or shot bag out of an old leather couch cushion. Use the bag in place of a dolly to support the piece while you work out the blemish. The bag can conform to the basic shape of the part, in a way that a rigid dolly cannot. In the case of fenders, a shoemaker's anvil isn't a bad choice, either.
on the right side looking at the photo that is the part that is stretched. you want your dolly under that part and hit the high spot/stretched part with the hammer. you want to push with the dolly when hammering.
one thing a great many people do not realize is the metal does not know which is the hammer and which is the dolly. so most people would hammer the indented part from the inside trying to push it back out. metal has a memory and wants to go back to the original shape, so you mainly want to hit where the metal has stretched and the center will pop back out pretty good.
if this was a fender that was going to be painted rather than chrome a person could get it perfect with the proper techniques. being chrome would make that more difficult but you can at least get it much better
Looks like aluminum to me.. I’d start inside at the center not hard but lightly then once it’s up a bit ( should pull most of it up) don’t pound it on a dolly till it’s near the right curve.just pound it out lightly but firm otherwise you will stretch the metal by flatting it out...I’d work on the edges till it’s up.. it’s gonna look lumpy. Then dolly it out from the inside till most of it looks level. Next check for curvature...should be close. continue to work it out till all of its out. If a small dent won’t come out then you have to slightly pick it out. One or two small picks...If it’s too high you’ll have to shrink it with a pick again on the outside. My guess if it’s aluminum you will have to pick an file it out lightly till it’s smooth there will be some small stretched spots.
not to sound rude, but don't listen to these other peoples advice. I bought my first set of hammers and dollies 40 years ago. worked at a body shop for a few years doing restoration work. I've had my own "hobby" shop here for 22 years. watched all the videos and read all the books. this is not my first dent.