Using an Internet Browser, go to https://mysignins.microsoft.com
Once at this screen, use the menu on the left and CLICK on "Security Info"
Add the second contact method – office phone or cell phone, or Authenticator app if you selected to use a phone initially.
How to use the second contact method
When signing in you should be prompted to Approve Sign In Request
Click the Sign In Another Way link to view other methods
Your other methods will be displayed, select the method you would like to use
