Remove the rear half of the flare carefully. 2 nuts inside, a plastic pop in clip and the screws holding it to the mudflap and the body.
Clean it off well.
Remove the taillight
Disconnect and Pull the harness out of the way
If you don't go with the fitz Rod gun that was mentioned you can still get a good amount out city a body hammer and Dollie set as well as a panel slapper... Keep in mind that the metal is now stretch on the corner and it will not look perfect without a lot of skill. At any rate, start in the center of that pushed in corner with a crowned body hammer and give it some medium to soft controlled hits and work outward in a spiral like manner until you're just past the outer edge by maybe 1-1.5 inches if possible.
Then Use the panel slapper in the same manner...can't tell it there is a crease, if so then start on the crease working from the most pushed in spot toward the least do this in several soft to medium passes for best results... If you have to go up and down the length 50 times to get it out to level then do it.
There might also be damage on the a on the sub structure of the panel.. Pull the plastic from around the inside of the wheel well and see if there is any visible buckling and damage, if there are buckles in the sub structure you need to hammer those out as you go along also.
A little buckle, a little panel back and forth until it's good.
from the inside, pulled the interior panel, removed lights, ensured wires were out of the way, shoved a 3' piece of 2x4 in and used leverage to push the panel out. It would slide up the panel and push it out OK. I used smaller pieces and a big hammer to shape it a little more and smooth out some creases. Near the bottom of the panel I placed the 2x4 as far down as I could get it and started beating the end of the 2x4 to pop it back out.
a lot of pounding and swearing, but boy did I feel good after! and like I said, it's not near new, but in my mind it's fixed because it's no longer concave.
photobucket wasn't cooperating so they're links to shared pics on google drive.
I had a spare hour during the day today. It may not look better, but it's better. Not professional or even passable yet, but an hour, a scissor jack, bottle jack, hammers and 2x4s have made a little improvement to the upper panel and the alignment of the lower. Previously the lower panel was 4-5 inches inside the outer wall of the tire and mudflap, hence the mud spray. Now it's almost aligned with the outside.
I think I can get it much much better with some more time, tools, paint and beer.