I just went and looked inside my car, it has a seam in the headliner about 8 inches from the back , the headliner is tacked up to a roof bow or other wood above that seam -perhaps yours came loose
My wife has a handheld clothing steamer that i was going to borrow for some upholstry work ----but the store it came from is along ways away, it's 220-50cycle
The right side of my headliner sags away from the wood bows! There's NO stitches holding the fabric tacking strip to the headliner. Apparently, "they" used an iron on strip & it came loose. (CHEEP SHITS!) I don't know who made the kit, the rest of it looks good. Upholstery was installed in 2002 & looks like it was done last Tuesday. Bill W.