Lexmark C910 User Reference Manual page 56

2
Press the metal plate down until it locks.
3
Squeeze the left guide and slide it to the position for the size paper you are loading.
4
Release the paper guide.
Note: The position of the left paper guide tells the printer the size of the paper in the tray.
If the left paper guide is in the wrong position, you may experience paper feeding
problems or incorrect page formatting.
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