i tried to pull the tabs and one of them snaped off. how can i unlatch the back seat from its hooks?
Did you lock the seatback locks?
If you did, that would explain why the seatback would not release when you pulled on the knobs.
The cover for the seatback is held in place by a single long zipper. The zipper is removed at the end of the assembly process. You can pull the zipper apart, to gain access to the seatback release mechanism (make sure you unlock the seatback locks this time), but I don't know how your going to zipper the seatback cover back on when you're done.