Always a tricky one this! You can try very gently bending it back after heating in hot (NOT boiling) water, or with a hair drier. But this can possibly cause warpage across the chord.
Alternatively, if there's room to fit a spar of some type, either very stiff plastic, or timber, or metal, then that can be glued to one side, the wings taped, and then gently pulled into shape with gentle heating. Once straight, then glue immediately and clamp the length of the warp.