On a recent trip, the middle seatbelt in the back of my Accord was knotted and used to help keep a large cooler in place on the backseat. When the cooler was freed up, the knot in the seatbelt couldn't be undone before it rachetted to the top and we can't undo the knot now and use the seatbelt. Any suggestions on how to fix it? If I need to take it to the shop or dealership for repair, how much would cost?