Hay Versey
One time I had a puckered in Kawasaki 750 LTD fuel tank that need to be "UN-PUCKERED".
So , I put a thick sheet of plastic over the refueling hole and closed the lid. Then , I put the air hose to the fuel petcock with a good clamp and turned the air compressor on .

Well ,

as the air pressure rose near 100 pounds the PUCKERED area did pop back out .
But
Next time I fill it up ... it held more ... I don't remember how much more but the next time I had the fuel tank off I saw why !
The web of the tank had puffed out a noticeable amount.

......
I suspect , ??? while the tank had pressure on the inside a person could use a torch to weaken the area they wanted to expand outward . ???