Brother DCP-L8410CDW Online User's Manual page 583

NOTE
To avoid print quality problems, DO NOT touch the shaded parts shown in the illustrations.
5. Make sure the green lock lever (1) is in the release position, as shown in the illustration.
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6. Gently slide the drum unit into the machine until it stops at the green lock lever.
7. Turn the green lock lever clockwise to the lock position.
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