It happens. It really only serves as chafing protection for the sewn threads. That's it's only job in life. Best fix is fresh shrink tubing. Somewhere between 1-1.5" tubing should suffice depending on the thickness of how it was sewn. Clear is best so you can keep an eye on that sewn portion. If the old shrink tubing just slid off and is not ripped, you can try to just zip tie it back in place to hold it snug. Can even hit it with some more heat (hot air, not a torch or your lighter) to get it to shrink down some more.