Are you talking about the zipper around the door windows? If so, I just stay away from them because you can't remove the skeleton frame from the canvas. My sewing machine foot won't lift high enough to clear the frame. But if you have a long arm sewing machine with a foot that lifts high enough, it's doable.

If you remove your presser foot, i will be easier to get the frame under the machine. I would recommend that the customer should get new doors as the old ones are not going to last much longer after a repair.