Go to the RumbleTalk chat plugin settings, then click on the Settings button.
Go to Users.
Then, Add New User/Admin.
Fill in the form and choose where your administrator will only be for that specific chat room or all your chat rooms.
Take note: Only add users in your chat room setting if you wish to set them as an administrator of the chat room. This will allow other WordPress users from your database to login with the chat automatically and set passwords only for the administrators.