Canon imageCLASS MF7280 Reference Manual page 222

3
6
4
6-8 Paper Drawers
Detach the end guide and reattach it to the slots with the mark
indicating the desired paper size.
Detach the end guide by pressing down and forward. Align the end guide with
the mark indicating the desired paper size. Reattach the end guide by tilting it
forward and inserting the tabs at both ends into the slots. The end guide should
then be returned to its vertical, upright position.
NOTE
Attaching the end guide while pressing down the point indicated with 'A'.
Lift the lock lever on the side guide to its upright position and
slide the side guide to the groove marked for the desired
paper size.