You can go back to an instant messaging (IM) conversation, audio or video call, or meeting to restart it. When you resume a meeting, it opens the meeting window back up. When you rejoin an IM conversation or call, Skype for Business (Lync) sends a conversation request to the other participant(s) to join back in.
Important: Conversations are saved only if you’re using Outlook with Exchange.
In the Skype for Business (Lync) main window, click the Conversations icon (above the search box), and then click either All (to display your 100 most recent Skype for Business (Lync) conversations) or Missed (to display recent conversation requests that you were unable to respond to when they came in).
Find and double-click the conversation that you want to resume. To add audio in a conversation window, click the call button.