As an admin, you can log in to the Agent interface as any Agent (including other Admins). This can be useful for troubleshooting purposes.
Note that when you are logged in as an Agent, it’s exactly as if you have signed in with their account name and password. For example, if the Agent doesn’t have Permission to alter their own notifications, you won’t be able to alter them either. If you send a response to a User, it will appear to come from the Agent who’s account you are using.