Oki C 5300n - Manual (Page 135)

C5300 Replacing Consumables • 135
7. Holding the cartridge by its top center with the colored release
lever to the right, insert the left end of the cartridge into the top of
the image drum, pushing it firmly against the spring on the drum
unit.
CAUTION!
Do not touch the toner release lever until the toner cartridge
is installed in the image drum. If you do, it will open the toner
release slot and spill toner.