what are you a scottsman? covering shrinks too much to be reused again. if the pieces are in contact with each other you could make a small hole, repeat very small hole and drizzle some thin ca into the joint and hope that will tighten up the loose balsa. then you could place a small patch of trim or maybe the proper colored packing tape to seal the slice. If it has never been flown there should be no residue on the covering so everything should seal nicely. make the slice on the side away from the exhaust.