Change a user’s email to a federated domain in Apple Business Manager
If you have successfully linked Apple Business Manager to your Microsoft Azure AD domain, you can change an existing account so that its email address and Managed Apple ID are identical. An exception is that an account with a role of Administrator or People Manager cannot use the same address for both.
Change a user’s email to a federated domain
In Apple Business Manager , sign in with an account that has the role of Administrator or People Manager.
Tap Accounts in the sidebar, search for an account in the Search Accounts field, then select the account from the list. See Search for user accounts.
Tap Edit, change the email address, tap OK to also change the Managed Apple ID to match the email address, then tap Save.
That user can now sign in with their Managed Apple ID and their domain password.