There's no easy way to change the customer's email address.
For the Jira Service desk administrators to have the ability to change the customer's e-mail address and retain all the issues that is in progress.
Try migrating the customer account to "Atlassian account":
- Login as a site-admin
- Operate migrate to Atlassian account for the portal customer account in question
- Optional: maybe you want to disable the product access for the account. But make sure to keep Has access on site enabled.
With that, now the user can change the email address at https://id.atlassian.com/manage-profile/email.
Besides, consider adding yourself as a watcher to be kept informed as to the state of this feature request moving forward. With that way, if our development team updates the ticket, you'll be notified via email.