Enable Office 365 Two Factor Authentication

https://www.microsoft.com/zh-cn/account/authenticator

https://support.microsoft.com/zh-cn/office/%E5%B0%86-microsoft-%E8%BA%AB%E4%BB%BD%E9%AA%8C%E8%AF%81%E4%B8%8E-microsoft-365-%E9%85%8D%E5%90%88%E4%BD%BF%E7%94%A8-1412611f-ad8d-43ab-807c-7965e5155411#ID0EAAEAAA=_%E6%AD%A5%E9%AA%A4_1

Download and install 'Microsoft Authenticator' on your mobile phone.

Login your Office 365

click [View Account] on top-right

choose [Security Info] on the left menu bar

there is a list of your authentication methods

check if 'Microsoft Authenticator' is listed, if not, click [Add method]

choose 'Authenticator app'

click next a few times until you see the QR code

scan with the microsoft authenitcator app and then click next

it will then ask you to 'approve' it on your mobile phone

check your mobile phone and approve it

there should be 'microsoft authenticator' in the list

Click the [change] button to change the 'default sign-in method' to 'Microsoft authenticator'

Then try logout and login again, after you enter the password, it should ask you to approve it on your mobile phone