Can I block someone else's service account?

As an administrator, you cannot block users. However, there are two alternatives:

Delete users

You can delete a service account. Doing so will permanently delete the service account. If you wish to grant permissions to that person again at a later time, you must create a new service account. For more information, click here:How do I delete a service account?However, it is not possible to simply temporarily suspend the service account.

Revoke rights

Instead of deleting a person's service account, you can revoke their permission to use online services. You can revoke all permissions or just specific ones. Here's what you need to do:How do I assign permissions and roles to others?