Dell 3000cn Color Laser Printer User Manual page 162

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.