Change a user’s email to a federated domain in Apple Business Manager
If you’ve 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, Site Manager, or People Manager can’t use the same address for both.
Change a user’s email to a federated domain
In Apple Business Manager , sign in with an account whose role can make changes to other accounts, then click Accounts in the sidebar.
Select the account whose email address must be changed, then click Edit.
Change the email address, click OK to also change the Managed Apple ID to match the email address, then click Save.
That user can now sign in with their Managed Apple ID and their domain password.