Epson B813112 Use Manual page 16

The right dial controls where paper stops when it is first loaded
from the feeder. The left dial controls where double-sided
originals stop during scanning of the second side.
mm mm
If the upper portion of the scanned image is missing, turn the
dial clockwise. The position changes in 1 mm (0.04 inch)
increments.
If the lower portion of the scanned image is missing, turn the
dial counterclockwise. The position changes in 1 mm
(0.04 inch) increments.