Dear @Ace King
I understand the issue. The important point is that Microsoft Authenticator does not send you a separate SMS/message containing a code. If your school account is still registered to the old device, installing Authenticator on the new phone does not automatically transfer that registration.
If you can still sign in to your school account using another method:
- Go to Security info
- Select + Add sign-in method > Microsoft Authenticator.
- Follow the prompts and scan the QR code with Authenticator on your new phone.
- Once the new phone works, remove the old Authenticator registration.
Microsoft documents this process here: How to add your accounts to Microsoft Authenticator
If you cannot sign in because Authenticator is the only verification method, you cannot generate the required verification code from the new phone by itself. Because this is a school account, you will need to contact your school’s IT/help desk or Microsoft 365 administrator and ask them to reset/re-register your MFA (Authenticator) method. They can then allow you to register the new phone.
If you still have the old phone and it is usable, don’t delete the old Authenticator registration until the new one has been successfully registered. Microsoft also recommends completing the transfer before removing the old device. Please refer to this document: Transfer Microsoft Authenticator account entries to a new phone