You can enable the barge-in feature for users so that they can use a Feature Access Code (FAC) to answer someone else's phone call or barge in on a call they've already answered. This feature can be used across locations that you've created in Control Hub.
From the customer view in https://admin.webex.com, go to Users, and then select the user you want to modify.
Select Calling, go to Advanced Call Settings, and then select Barge In.
Turn on Barge In, choose whether you want the phone to play a sound when someone barges into a call, and then click Save.