How to change Office 365 Authentication Method
You will need to install the Microsoft Authenticator app for your model phone.
Log into your O365 account at https://office.com/
In the top right corner, click your picture and choose View Account
Then click Security info
You will see the default sign-in method that you are currently using. Click Add method to add a new MFA
Click the drop-down arrow to see your choices. Choose Authenticator app to add it as your authentication method. If you prefer, you can add a new Phone number as well.
If you still need to install the app, you can click here to download it. Then click Next
Click Next to Setup your account
Open the Microsoft Authenticator App, Click Add Account or the +, choose Work or School account then scan the QR code (IPhone users will need to allow the Camera to have access to scan the QR code)
Click Next
The authenticator will send a test authentication to your phone to approve.
Once you approve it with your phone, you will get a Notification Approved
Click Next and you are done.