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I understand you're unable to sign in to your school account because you changed your phone and now don’t have access to the Authenticator app.
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In this case, kindly ask the one who is having the Admin permission to help you reset your MFA settings through the Microsoft Entra Admin Center.
If you’re unsure who the Admin is within your school, you can find guidance on locating them here: How do I find my Microsoft 365 admin? - Microsoft Support
Please have your administrator follow the steps shown in the following article: Manage authentication methods for Microsoft Entra multi-factor authentication - Microsoft Entra ID …
- Sign in to the Microsoft Entra admin center as at least an Authentication Administrator.
- User > all user. Select the user you want to act on, and select Authentication methods. then select Require re-register of multi-factor authentication.
Require re-register MFA: This disables all previous authentication methods. You'll then be prompted to configure a new MFA authentication method the next time you try to sign in, so you can add a new authenticator app.
Please feel free to correct me if there are any misunderstandings. Kindly let me know if there are any further concerns or if you need more assistance. I am happy to help!
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