What should school administrator do when teacher is left from the school but school administrator forgot to disable user login account?

To disable the staff user account who has left school, please perform the following:

Step 1:
Reinstate staff account, go to Basic Module ~> Staff Mgmt ~> Leaving School ~>Reinstate.

Step2:
Delete/disable the login account, please refer to What should school administrator do when a teacher is being transferred/left school?

Step 3:
Transfer (Basic Module ~> Staff Mgmt ~> Transfer ~> Create) and verify (Basic Module ~> Staff Mgmt ~> Transfer ~> Verify) the staff to revert the teacher to transfer status.