Look at how they attached the material to the camper's rail. Mine has a screw at each end. You would have to remove those screws before tugging the material over to the roller end.
You may also need to insert a thin cutting tool into the roller end to cut the plastic rod (and remove it in pieces) to allow the material to slide toward the end. Do not over do it as you will need some space to allow the awning materiel some room to roll up without binding.
Once square and able to roll up without binding; pop rivet the roller end of the awning so it does not shift.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW