Choose "Add a new way to signin or verify", select "Email a code",
follow instructions to add your backup email
Expand old backup email and click "Remove"
Choose "Add a new way to signin or verify",
Select "Use an app",
In new window click blue text "set up a different Authenticator app",
"Next",
"I can't scan the bar code",
In new window copy and save secret key,
Use 2fa.live to get 2fa code,
Enter code on microsoft page,
Click "Next"
Done, you've changed password, backup email and 2fa key!