Before registering a user using Microsoft/Google authenticator, enable 2FA for the user. Refer Enabling Two Factor Authentication
To register a user using Google Authenticator
Click on the user initials on the top right corner of the NSM and click User Profile.
Click User Registration using QR Code for Authenticator Apps link.
Scan the QR code in your Google/Microsoft Authenticator App and the user will get registered in the authenticator app.