If you need to disable an OS user account, you can expire the account using usermod --expiredate 1. For example, to disable the account for user tom:
sudo usermod --expiredate 1 tom
For more information, please see man passwd and man usermod.
If you need to disable a SSO (Sguil/Squert/Kibana) account, you can use the so-user-disable command:
sudo so-user-disable
If you later need to re-enable this SSO account, you can use the so-user-passwd command to reset the password which will automatically re-enable the account.
If you've enabled Elastic authentication, you can manage Elastic user accounts in Kibana under Management --> Users.