When I had a Bodhran which could not be tuned, sometimes too much moisture in the air caused the same problem of the skin not being taut. Some non permament remedies are: lay the drum down under the hot sun with the head up till it tightens up to the desired tuning; place a heating pad over the drum head; place the drum near a light bulb.
I've had some folk drums which have (skin) heads held down by strips or laces of the same skin which have since dried out & one would have to wet them down & soak them to adjust the tension. It often results in ruining the wooden drum barrel and the laces, & trying to remove the dried ties sometimes causes them to break. Good luck!