yeah, you need to fold the seat back down (lift the bottom to the upright position first, then pull up on the knob on the seatback, close to the windows) you may need to remove a strip (could be metal or plastic) that goes between the seat back carpet and the cargo carpet and holds both down, but if someone was in there before you, it may already be gone... just behind the seat back, lift/fold back the carpet, and you should see the access covers - there will not be any sticky material (sound deadening) over top of them.
in a wagon, the access covers are BEHIND the seat, in the cargo area - not under the seat.