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 Between-User Permissions, and then select Barge In.
Turn on Barge In, choose whether you want to make the ongoing call a conference call.
Then click Save.