If you want to mention a specific role, you @ mention it like you would if you were mentioning a user. At this time, we currently support the following:
@everyone – Pings everyone online in the room. For mods only.
@djs – Pings everyone that is currently in the room queue. For mods only.
@mods – Pings everyone with the role Mod or higher. Available to all users.
@admins – Pings all admins online in the room. Available to all users.