Apparently, from your last post, the wing is not finished yet. Jig it up so that it is flat and finish the wings. How big is this wing?

You should be able to remove some warp after the wing is done by shrinking the covering. You may have to do it more than once. Normally, to remove a warp, or add washout, you have to warp the wing in the opposite direction more than the amount of the warp. Be sure to heat both sides of the wing when trying to remove the warp with the covering. One side will shrink and the other will stretch when the heat is applied. A second set of hands is helpful.

Once the warp is out, let it set a day or two and check it again. It might take more than one attempt before it sets in the position you want.

The post that suggested ammonia will work too, if the wing has a bad warp. Just be sure to jig it and not induce a bow or some other unwanted twist. If you use this method, be sure to let it completely dry before removing it from the board.