If the wing has a slight "BOW" to it, but it is not "WARPED", you have two choices...

1, leave it alone, it will fly fine.

2 cut off the sheeting, top spar and shear webs, and start over.

If the wing is bowed, the top spar is shorter or longer that the bottom spar. If you go wetting things or putting weights etc., you are probably going to WARP the wing, which is MUCH WORSE than a bow!