Canon NP6551 Operator's Manual page 187

Remove the paper remaining in the fixing unit.
6
Following the directions in the display, turn the
7
knob on the duplexing unit in the direction of the
arrows.
MEMO: ●
Perform this procedure when paper is jammed
between the fixing unit and the duplexing unit. Be
sure to follow the directions in the display.
Push the fixing unit back into the main unit.
8
Return the green lever to its original position.
9
When the lever is pushed in as far as it will go, a
tone will sound.
6-13