Step::1 Login to your WHMCS account with username and password.
Step::2 Navigate to the “Setup” tab.
Step::3 From the drop-down list choose the option “Staff Management”.
Step::4 Select the option “Two-Factor Authentication”.
Step::5 Click the “Activate” button next to the type of two-factor authentication you wish to use.
Step::6 Click over Save Chnages.
Check out the video tutorial on the topic. You may read out the blog as well.