GMC 2004 Yukon XL Owner's Manual page 28

To fold the seatbacks on the bucket seats, do the
following:
1-22
1. Pull up on the strap
loop located at the rear
of the seat cushion
and pull the seat
cushion up. Then fold it
forward.
If the seatback cannot fold flat because it interferes with
the cushion, try moving the front seat forward and/or
bringing the front seatback more upright.
2. Pull the seatback
release lever up and
pull the seatback
forward. Then fold it
until it is flat.