Chevrolet 2004 Avalanche Owner's Manual page 155

3. Roll the cover toward the front of the vehicle. The
plastic lip (E) will release from the siderails (C) as
you roll the cover forward.
4. Stow the cover using the buckles and the straps
attached to the front rail.
You can also store the tonneau cover outside of the
vehicle or use the storage bag included.
2-83