[morzh]

It's a theory but if you could use a thick cardboard (well you might get lucky and have a cone-shaped solid object at home with the surface curvature matching the dial but it is not likely) to create a cone with matching angle and curvature, and then while heating the dial keep pressing it against the cone and then leave it taped around (having made sure the tape will not lift the text off it)) that could be a way to remove the warpage.