Dell 3100cn Color Laser Printer User Manual page 86

6. To insert the toner cartridge, align the arrows on the cartridge with the corresponding arrows on the printer. Guide the cartridge in until it snaps into
place, and then push down the handhold to lock the cartridge in place.
7. If replacing just one toner cartridge, close the front door and you are finished.
NOTE: Make sure the toner cartridge is installed correctly. Otherwise, the front door cannot close firmly.
8. Repeat steps 4 through 7 when inserting the remaining cartridges.
Basic toner cleaning instructions
A cleaning rod for cleaning inside the printer is installed on your printer.
1. Open the front door.