I asked AI because I had the same issue. this is what it said to do.
- Log in to your Microsoft 365 account (from a computer)
Go to https://mysignins.microsoft.com/security-info (or you can get there through your Office 365 account → Security info under your profile).
- Add a new sign-in method
Click Add sign-in method → choose Authenticator App.
Select Next and you’ll see instructions.
Microsoft will display a QR code on your computer screen.
- Scan the QR code with Microsoft Authenticator
On your new phone, open the Authenticator app.
Choose Add account → Work or school account → Scan QR code.
Point your phone’s camera at the QR code shown on your computer.
- Test and confirm
Microsoft will usually ask you to approve a test notification in the app.
- Once you approve it, your Authenticator is re-linked to your account.
- Log in to your Microsoft 365 account (from a computer)
- Go to https://mysignins.microsoft.com/security-info
(or you can get there through your Office 365 account → Security info under your profile).
- Add a new sign-in method
- Click Add sign-in method → choose Authenticator App.
- Select Next and you’ll see instructions.
- Microsoft will display a QR code on your computer screen.
- Scan the QR code with Microsoft Authenticator
- On your new phone, open the Authenticator app.
- Choose Add account → Work or school account → Scan QR code.
- Point your phone’s camera at the QR code shown on your computer.
- Test and confirm
- Microsoft will usually ask you to approve a test notification in the app.
- Once you approve it, your Authenticator is re-linked to your account.