Depending on the type of wing construction it may be next to impossible to remove the warp
just using heat on the covering.

If the area from the spar forward is fully sheeted & it has a full depth spar or two webbed
spars once the wing is glued together the boxed section at the front is mechanically rigid.
If this is the case you'll have to remove the top or bottom sheeting, pin the wing flat &
glue the sheeting back on. [&o] - John.