Kyocera Mita FS-1050 Operation Manual page 141

Toner Container Replacement
7
While pushing down on the toner container, push lock lever #1 to the
lock (LOCK) position. (Lock lever #2 is automatically locked.)
After the toner container replacement is finished, reset the toner counter.
See Resetting the Remaining Toner Counter
Note
Lock Lever #1
3-5
on page 1-75.