I too have had to pull mine and resew the seams due to the thread breaking down.
There is a long loop or flap that is sewn over down the edge that attaches to the motor home, and another that is trapped in the roll up mechanism. You have to slide a thin flexible rod or a tube into the loop and slide all of that into a cavity and the rod or tube prevents the loop from pulling free.
If the loop has failed you have to take it off and have it re-sewn. Anyone with a sewing machine can fix it as it is right at the edge, the cross seams are a different story. Had to re-sew them by hand.
To make the job a little easier yo can go to anyplace that sells hydraulic stuff (hose and fittings) and get a length of thin tube. I think it was 3 milimeter, but if you take in a bit of what it came with they can give you a slightly smaller size - trust me, this makes it easier to put back.
The trick is unwinding the spring and not hurting yourself. Check out this link:
https://www.toughtopawnings.com/blog...d-slide-topper