You can upgrade Webex Calling licenses to Professional license to Basic all from Control Hub. Upgrading licenses maintains user’s feature settings and assigned device/ clients.
If you upgrade a user's license to Professional, then you'll want to follow these steps to add more devices to that user. Clients and applications are automatically assigned to users you upgrade.
Find out more about features that are available with the basic and Professional licenses in this table.
Upgrade a user's Webex Calling license
From the customer view in https://admin.webex.com, go to Users and select the User whose license you want to change.
Select the Professional, and click Save.