How can configure where admins can view and reply to live chats?

I can't figure out how to respond to someone who's posting on live chat (I'm using the bottom corner chat). When anyone signs in to chat a message always populates stating that a moderater has closed the session?

I'm confused 1stly on where I, the site owner and other admins that will be responding to chats, goes to reply to live chat.

Secondly I don't know why on the user side I'm getting the moderator has closed the session message

Thanks ahead of time for your assistance on this

-David