I have fixed warped wings, stabs of various types -including those like yours

Pattern planes at one time were glassed and painted and this same situation occasionally arose.
The trick is to determine which way the twiat must be made-then - on the bottom surface, make a diagonal slit thru the covering from LE to hinge line
this MUST be done such that the twist will close the slit when pressure is applied.
Block the stab into position after feeding in slow thin drying epoxy along the entre slit- then wiping excess awy with a damp rag -or with de natured alcohol
The result will be a a hairline crack on the surface if you were careful.