Using Microsoft Authenticator with Office 365
Download and install Microsoft Authenticator app
Download and install the Microsoft Authenticator app for Android, iOS or Windows Phone.
Set up the Microsoft Authenticator app
Open a browser on your computer and go to portal.office.com. Sign in to your Office 365 for business account.
Use these steps if you see this screen:

Use these steps if you see this screen:

Choose Settings > Office 365.
Choose Security & Privacy > Additional security verification > Update my phone numbers used for account security.
In the drop down box under What's your preferred option, choose Notify me through app.
Check the box for Microsoft Authenticator app, click Configure.