Dell 5100cn Color Laser Printer User Manual page 60

9. Pull the printer's tray out until it stops. Hold the tray with both hands, lift the front slightly and remove it from the
printer.
10. Insert the four screws provided into the four holes inside the printer and tighten them with a coin to secure the
printer to the optional 500-sheet tray module.
NOTE: Make sure the screws are firmly tightened.