GMC 2007 Yukon Denali Owner's Manual page 19

The seatback will fold forward automatically.
Leaving the seatback in this position creates a
flat load floor.
If the seatback cannot fold flat, try moving the
front seat forward and/or put the front
seatback in the upright position.
3. Lift the same lever
again to release the
rear of the seat
from the floor.
The seat will
tumble forward.
19