Using the mention feature
Use the user mention feature to reach out to one or more selected chat participants and address your message to them.
You can place the mention at the beginning, middle or end of your message.
Open the required chat box.
In the text input field, insert the @ symbol.
Result:
The @ Mention list is displayed. It contains the avatars and nicknames of the chat participants.
In the @ Mention list, select the nickname of the required chat participant:
Use the direction keys to select the nickname, then press Enter
Left-click on the nickname
You can start typing a chat participant's nickname to narrow down the selection options.
To mention another chat participant in the same message, repeat steps 2 and 3.
Type in your message.
Select the
button or press Enter to send your message.
Result:
The mentioned users see the notification icon 
in the chat dropdown list and on the Query Management popup, next to the chat they have been mentioned in.