Olivetti C3520MFP User Manual page 88

11. Insert the left end of the cartridge into the top of the
image drum unit first, pushing it against the spring on the
drum unit, then lower the right end of the cartridge onto
the image drum unit.
12. Pressing gently down on the cartridge to ensure that it is
firmly seated, push the coloured lever (1) towards the
rear of the printer. This will lock the cartridge into place
and release toner into the image drum unit.
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