Hi Rangerman, I had a twisted built up wing once and the only cure was to strip the covering, remove the shear webs, and re-install new shear webs with the wing twisted to the correct position + a little bit more. It held for a couple of years but the twist slowly returned. Ideally the leading edge sheeting should have been removed as well because that locked in a fair bit of twist.

If you're really lucky and the wing is really flimsy then shrinking the covering will work, but it's a really cheap and nasty way of doing it and probably only suitable for RES glider wings.

I got lucky with a set of foam core wings, the twist was minor and the sheeting had been attached with a water based wood glue so I was able to steam iron the twist out of them, then recover.

Cheers
Brett