When you change a user’s email address, they'll have 15 days to verify if the new email address is correct. If the user doesn't verify the changes, then the email address changes back to the original one.
If you use Cisco Directory Connector for user synchronization, you can't change a user's email address in Control Hub. You must manage user accounts from Active Directory and then resync the changes to Control Hub.
From the customer view in https://admin.webex.com, go to Users, and select a user.
Click Edit next to the user's name.
Under Email Address, enter the new email address.
A confirmation email is sent to the user’s old and new email address to verify the changes.