Replace/repair any damaged ribs. Wing sheeting can be made to bend easier if it is wet. Water with a little Ammonia in it, dab it on and try to curve it around, don't try to do it all at once. Bend it a little around and hold in place with rubber bands. Apply a little more water mixture and tighten (or add more) rubber bands. Steam also helps to make it curve better(no ammonia, don't want to breathe) I know you are bending along the correct grain? Be sure to use the orig thickness of balsa. Once sheet has taken it's curve let it dry in place. AFTER dry, glue into place. This all may take a while, again-don't rush