Canon MB5400 Series Online Manual page 1098

3429
Cause
First side printing is complete when manual duplex printing.
What to Do
Prepare to print the other side.
Keeping the printed side facing up, rotate the paper 180 degrees so that the front edge of the printed
paper faces away from you and fit the paper back into the cassette 1.
When ready, tap OK on the touch screen of the printer.
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