If it were me, I would try this:

Set the lower side of the stab on a can or stack of books to raise it off the ground and add some weight to the other side. Then work a heat gun around the glue joint (Carefully so as not to ruin the covering)

Worst-case senario, carefully cut through the underside of the stab (On the lower side) and add some thin shims to lift that side. Then epoxy the seam.