Dell 3010cn Color Laser Printer - Manual (Page 46)

6. Attach the trays together by installing the optional tray you just removed on top and inserting the two screws provided. Tighten the screws until they
are secure.
7. Place the printer on top of the tray module(s).
8. Lock the tray(s) into place by removing the top tray from the tray module and rotating the locking mechanism as shown in the graphic.