Brother DCP-8040 User Manual page 104

4
Gently rock the toner cartridge from side to side five or six times
to distribute the toner evenly inside the cartridge.
5
Remove the protective cover.
6
Insert the new toner cartridge in the drum unit until it clicks into
place. If you put it in properly, the lock lever will lift automatically.
Toner Cartridge
TROUBLESHOOTING AND ROUTINE MAINTENANCE 7 - 27
Drum Unit