From the customer view in https://admin.webex.com, go to Settings, scroll to Integrations and then click Manage.
Find the correct integration for your release of Webex Expert on Demand:
In the Overview window, choose Allow access.
Toggle Access for new users to On, click All users to give this permission to all your users, and then click Save.
Webex Expert on Demand | Allow Access to the Integration in Control Hub
When you restrict user access to integrations in Control Hub, you must include the Webex Expert on Demand integration in your allow list.