Click Start, point to All Programs, point to Microsoft Lync Server 2010, and then click Microsoft Lync Server 2010, Group Chat Admin Tool.

In the Chat Rooms list, click the chat room, and then click the Members tab.

The list on the Members tab includes everyone who is a member of this chat room. Names in regular font are members of this particular chat room. Names that are unavailable appear dimmed and are members inherited from the parent category’s membership list.

Click Add, and then do the following:

• In the Search For box, type a name or part of a name to search for, and then click Search. To limit your search to only exact matches for your search criteria, enclose the search criteria in quotation marks.
  
  Because the membership of a chat room or category must be a subset of its scope, only names in the scope are returned.
  
  
• In the list of names that match your query, click one or more names, and then click Add.
  
  
• When you are finished adding names from the list, click Close.
  
  

(Optional) To remove a user or group from the membership list, on the Members tab, click the name in the list, and then click Remove.

When you are finished making changes to the membership list, click Apply.