There are several adhesives suitable for fabric such as Loctite vinyl, fabric & plastic; E6000; Sew No More; or, Patch Attach which you might use. You might try taking two stiff wooden slats slightly longer than the length of the separation and two or (better) three clamps and, with the zipper open, spread a small amount of your chosen adhesive on the portion of the zipper that you want to adhere to the fabric (you don't want to put on so much adhesive that it squeezes out when you clamp it), put a wood slat on each side and clamp it all together. You can probably get away with using spring loaded squeeze clamps but you can use whatever clamps you have on hand.