Cadillac GMC Yukon Denali 2005 Owner's Manual page 26

3. Lift the rear of the seat up from the floor and push it
forward. You will not be able to unlatch the seat
from the floor unless the seatback is folded down.
CAUTION:
{
If the support rod is not properly engaged, the
folded third row seat could come loose in a
sudden stop or crash. That could cause injury
to people and damage to your vehicle. Always
be sure the support rod is properly engaged
when the third row seat is folded forward.
1-20
The seat will now remain in the upright position.
4. While holding the seat
forward, pull the
support rod out from
the retainer clips
and flip it down until it
latches into place.