From the customer view in https://admin.webex.com/, go to Users and select the user that you want to turn on call waiting for.
Under Services, choose Calling, and select Call Waiting.
Turn on Call Waiting.
Enable Call Waiting for Cisco Webex Calling
Let people take multiple calls at once. With call waiting, users can place a call on hold to answer a different call. When you are on an active call, a tone alerts you to an incoming call and you can choose to answer or ignore the call.