Buick Rendezvous 2003 Owner's Manual page 65

Second Row Center Position Bench Seat with Third
Row Seat Folded Down
If the vehicle has a third row seat and the seatback is
folded, there is an anchor on the back of the third
row seat for the second row center position bench seat.
Third Row Passenger's Side Outside Position
There is also a top strap anchor for third row
passenger's side outside position. Locate the anchor
symbol on the flap of carpet behind the seat. Lift up the
carpet to access the anchor.
1-59