The condition known as an “oil can” is often encountered when performing automotive bodywork. It can be described much like an oil can lid: the panel position is bi-stable and can flop in or out.
A common recommended fix is to use oxy/acetylene heat to create a localized hot spot that bulges the metal above the mean surface of the panel. The bulge can then be tapped down flat with a hammer and dolly to thicken the metal in that spot.
This takes away some of the “stretch”.
Propane can do the same thing although it is a much more crude method. Propane takes much more time to reach temperature, and the heat spreads out to a large area. While this lack of finesse may not be appropriate for finer detail work, it can work well and almost everyone has access to a propane torch…