Canon imagePRESS C1+ Reference Manual page 258

8
9
4
10
4-88
Adjusting the Machine
Remove the rear edge retainer, then remove the spacer that is stored in
the back of the rear edge retainer.
Loosen the two black adjustment screws on the outer size change
plate using a coin or something similar.
Insert the spacer (horizontally) into the space between the paper and
the outer size change plate.