I wonder when people are going to learn that there are about a hundred thousand different ways you could make a chat in PHP that would require different answers to the question you just asked.
We need more information. Tell us about how you determine who is an administrator. Surely if you wrote this chat you know that. If you didn't write this chat, please refer to our posting guidelines. The forum policy is to not assist with premade scripts unless the user is actively hacking the code and has a specific portion of the code as a problem. So if you were to give us the code for displaying your users, and give us the code for determining who is an admin and who isn't, it would be a simple task to combine the two.