Thought this might help others. Took me a bit of time and study to get this info.
My slide-out topper ripped in the wind and I had to cut it off on the side of the road. Naturally the factory set tension on the spring sprung out.
It was fairly easy to find information on how to put in the new fabric that I bought online. You just slide out the old fabric (after removing any set screws), cut the new fabric the same size, spray some silicon lubricant in the tracks, then slide the new fabric in both tracks at once, stepping it along. (I did this solo - I have a porch the right height that if I park close enough I can reach everything easily. My slide-out is only 6 ft wide; think you'd need help for longer slides.)
Once you have the fabric in there, you have to set the tension. Good luck if you try to read
the Dometic manual. I could not figure out from it if I could even adjust the tension of the spring with the topper assembly attached to the rig.
Finally found
an EXCELLENT post on another forum that tells exactly how to do it:
"Well, turns out to be quite easy, I just retracted the slide in to within 6" of the side, removed the one screw holding the roller bracket on the hex shaft, the 2 screws holding the hex shaft in the mounting bracket, pushed the hex shaft in to dis-engage the roller bracket while holding the bracket. Added 2 turns to the tension and re-installed. Took less than 20 minutes for both sides. Won't know if it helped or not until it rains again, but we'll see."
(re: "removed the one screw holding the roller bracket on the hex shaft" - mine was held in with pop rivet. I just drilled it out. Using a set screw now rather than rivet)
You have to do both brackets separately. Those instructions are for just tightening the spring. If you have to set the tension from zero like I did, you do 13 turns instead of just 2; that 13 is from p 4 of the Dometic manual linked above. It also tells you the direction to turn it for both the right and the left bracket. Then test it - open and close. If it isn't right, then either add or undo a couple turns.