I found this suggestion. Let us know if this works for you.
cut yourself a piece of 2x4 about 1/2" shorter than diameter of the pan's bottom, i.e., just short en
ough to fit flat in the pan if the bottom weren't warped.
Heat the pan.
Set the pan on a flat piece of concrete (a thick steel plate would be
better, but how many people have those sitting around?).
Put the 2-by in the pan and start whacking the heck out of it with a
hammer. Turn the board so every part of the pan gets flattened, but
concentrate in the center.
Let the pan cool, reheat and repeat.
If the crown is on the bottom, you have to find something big enough
to support the pan's rim, but which allows the handle to extend beyond
the surface -- so the pan sits flat; and of course, you'll want a 2-by
a few inches longer than the pan is wide.
If you're very thorough, you'll flatten both sides each time you