Warped Bottom Piece - How to Straighten

I have an old Folkcraft kit I am beginning to assemble. The bottom piece, solid walnut 7x32x2.5mm, is warped from side to side. It's a slight cupping. I can glue it on to the body in a concave or convex way, but I'd like to try to straighten it out a bit first. Am I looking at buying a new bottom, or can this be straightened out, and if so what is the best way to go about straightening it out? I paid $30 for this old kit, so if I have to buy a new bottom it won’t be terribly upset.