Buick 1995 Century Owner's Manual page 18

To raise the rear-facing third seatback:
If your vehicle is equipped with a roll-up cargo cover,
it
must be removed before raising the seatback.
1. Open the liftgate and lift the storage compartment
lid.
2. Fold
it
forward against the seatback.
3. Press down on the seat release levers (one on each
side of the seat), and allow the seatback to pop up.
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