Canon imagePRESS C800 Series Operation Manual page 206

Replace in the standard stacker / stapler the staple cartridge in the staple unit
Action
6 Gently push the staple case into the staple unit
and push down firmly into its place.
7 Close the front cover of the stacker/stapler.
The stapler unit may staple to reposition the staples.
206 Chapter 7 - Maintain the print system
CAUTION
When you close the front cover of the stacker/stapler, be careful not to get
your fingers caught. This can cause personal injury.
imagePRESS C800 Series