I found a used tow hook cover to replace my missing one but it had a huge bulge in the center from the tow hook poking it. The previous owner had put two small screws into the upper corners which kept if from popping out. Great idea.

Anyway, I set a 1500 watt industrial heat gun on the bench, facing me, and held the cover with it's back to the gun. Pushing the bulge back with my thumbs while the gun heated the backside the original contour was achieved in a minute.
Worked better than I'd hoped.

Sanded, painted in place with the rest of the spoiler (removed from car) and it looks great. Yes, I did zip tie it in place but also put the screws in the top corners as before. It's not coming off.
--
Erwin in Memphis, '88 745t 190,000 miles, '95 855t 92,000 miles