Click the "Activate night answer" icon in the toolbar.  

Call forwarding to the night destination is activated and the toolbar button changes to "Deactivate call forwarding" . 

You must still answer any waiting calls in the call display. Any new calls are forwarded to the night destination.

Click the night answer button in the toolbar.  

Call forwarding to the night destination is deactivated and the toolbar button changes to "Activate call forwarding" .