Dell 3010cn - Color Laser Printer Manual page 120

5. Lift the tab up 90 degrees and pull the toner seal straight off, keeping it parallel with the toner cartridge.
6. To insert the toner cartridge, face the label on the cartridge to the front and align it with the arrows on the printer.
NOTE: Make sure that the printer is turned on.
Inserting the cartridge
a. Guide the cartridge until it snaps into place.
CAUTION: Do not do not force the cartridge.
b. Push down the handhold to lock the cartridge in place.