what DaRock said ...An iron might work but you 'll do it easier with a monokote heat gun. Heat up both top and bottom of the "twisted" wing and put in opposite twist ...more than you think will do the trick.... an extra pair of hands helps. hold the well warmed wing in place with opposite warp until cooled . recheck by visually siting the wing center (bottom) and compare to wing's outboard (bottoms) reheat and twist if needed. Having the bottom of the wing tips a little "up" equally is called washout and is helpful on flat bottomed trainer wings.
good luck!