Chats can only be assigned or transferred to agents who are available, i.e. who are logged in and online. Agents who are logged out of Chat Desk will display as 'Unavailable'. Agents can also manually change their status from 'Available' to 'Unavailable' from the profile drop-down.
To view which other agents are currently online in your organization or business unit, hover over the headset icon in the top right corner of your screen. A list of all agents that are online is displayed.