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You can update your Legal name on your Microsoft Learn profile under Settings https://learn.microsoft.com/users/me/settings
If you have an exam booked, you will be shown a message and link to contact Credentials support https://aka.ms/credentials-support
You should have access to the Engage Hub
Try https://aka.ms/credentials-support which takes you to the Engage Center Hub, the location for certification support. I sometimes find that I need to use https://aka.ms/credentials-support twice.
If you do not see Microsoft Credentials selected against Product, create an account on the Engage Center Hub and then use the direct link https://aka.ms/credentials-support again.
If you see the message "You are currently logged in as a guested personal account, which may result in access issues on Engage Center." then click on "Sign in to Microsoft's tenant for Personal Users", select "Login to Engage Center", and then use the direct link https://aka.ms/credentials-support again.