Brother HL-4050CDN EN - Manual (Page 119)

Routine Maintenance
110
6
When you replace the drum unit with a new one, you need to reset the drum counter by completing the
following steps:
a
Turn the printer power switch back on.
b
Press the + or - key to choose Machine Info..
c
Press OK to proceed to the next menu level, and then press the + or - key to choose
Reset Parts Life
.
d
Press OK, and then press the + key to choose Drum Unit.
e
Press OK two times.