How to change primary email address for hybrid Azure/Local AD

We have a local AD environment and it syncs only one way up to our Azure AD environment. I created a user account locally and used an extention attribute value "O365" which causes the record to be created in our Azure AD environment. This is the normal process and has worked fine for 1000+ user acounts. The problem I am experiencing is this new user account I created shows the username@colgov.onmicrosoft.com address as the Primary email address in their Azure AD record. It should be username@lynchburgva.gov, which is our local/network domain, the colgov.onmicrosoft.com should be an alias and this address has always been created automatically when the record is created and synced for the 1st time to Azure.

I cannot change this in the Azure record because it is synced to our local AD, there is a small print note at the top of the user record window displaying this:
"This user is synchronized with your local ‎Active Directory‎. Some details can be edited only through your local ‎Active Directory‎." But the local AD record shows only one email address, username@lynchburgva.gov, which is the proper value and format.

Do you know why this is occurring for only this user and how I can reconfigure the account so the primary email address is the one with our domain name?

I apprecate your help.