Mine weren't as bad as yours, but I went through this with a set of wingtips that had been stored one inside the other for about 10 years.
I got them looking pretty good, but it took several hours with a heat gun and some pretty heavy weights. It's a very try-and-see-what-happens approach.
Basically, I heated the area I wanted to work on and then using a combination of weights, clamps, tape, string etc, held them in the position I wanted while they cooled. One of them off in multiple directions. It was too narrow overall, but the edges were pooched out like a teenage girl making duck lips for a selfie.
For that one, I made a wing cross section shape out of pink foam to stuff inside it, then fastened about a million cleco clamps on the edges. As I heated it up, I drew the edges together with string that was laced around the clamps like a shoe lace.
They came out okay and have been drilled and clecoed onto my wings for about a year now, so hopefully I don't get any surprises when I take them back off to get them ready for final fitment.
The whole process took several hours and was pretty frustrating, but better than buying new wingtips!
Here are a couple of pix that show part of my process