GMC 2001 Sierra - Manual (Page 157)

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2. Remove the three bows by gently pushing them
against the spring - loaded end. The three bows are
labeled front/center/rear to remind you in which
order to reinstall them.
3. To add cargo to the box,
remove all bows and the
back rail and stow
them safely.
To clean the tonneau cover, use mild soap and water.
If necessary, use a soft bristle brush to remove dirt
trapped in the grain of the material.