Brother Copier/Printer MFC-9970CDW - Manual (Page 91)

Routine maintenance
75
A
b
Hold the green handle of the drum unit.
Pull the drum unit out until it stops.
c
Hold the handle of the toner cartridge
and slightly push it toward the machine
to unlock it. Then pull it out of the drum
unit. Repeat this for all the toner
cartridges.