Chevrolet Avalanche 2004 Owner's Manual page 92

6. Turn both glass lock knobs (D), located at both top
corners of the storage pocket, to the locked
position. Push in on the corner of the rear glass to
allow the lock knob to engage more easily.
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Once both glass lock knobs are in the locked
position, the rear glass is securely stored.
7. Push both latch levers up to the locked position.
You should hear a click when each latch lever
locks correctly.
The rear seats can be returned to the normal
position when the rear glass is out and stored
properly in the storage pocket.