GMC Yukon Owner's Manual page 63

To fold and tumble the seat from the third row seats,
if your vehicle has them:
1. Make sure that there is nothing under, in front of,
or on the seat.
3. Lift the lever again to release the rear of the seat
from the floor. The seat will tumble forward.
2. Lift the lever, located
on the bottom rear of
the second row seat
on the inboard side, to
release the seatback.
The seatback will fold
forward.
Automatic Seat Release Fold and
Tumble Feature
The transmission must be in (P) for this feature
to work.
WARNING:
Automatically folding and tumbling the seat when
someone is sitting in the seat, could cause injury
to the person sitting there. Always make sure
there is no one sitting in the seat before pressing
the automatic seat release button.
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