Follow the below steps to enable multi-factor authentication for Office 365 account:
1. Visit webpage https://login.microsoftonline.com
2. Log in as Administrator.
3. Navigate to Office 365 Admin Portal by selecting the Admin icon or by entering the web address: https://admin.microsoft.com/Adminportal/
4. In the left pane of Microsoft 365 admin center, click Active users. In the active users list, select the account for which you want to configure two-factor authentication.
5. In the account options, under Account tab, click Multifactor authentication to manage multifactor authentication.
6. A list of Microsoft Office 365 accounts appears with information as Display Name, User Name, and Multi-Factor Auth Status. By default, the Multi-Factor Authentication status is “Disabled” for all accounts.
7. Select the required account again by selecting the checkbox against the user name, click Enable.
8. About enabling multi-factor auth pop-up message appears:
If your users do not regularly sign in through the browser, you can send them to this link to register for multi-factor auth: https://aka.ms/MFASetup
Copy and save this link as this will be needed to share with users to finish configuring multi-factor authentication for Office 365 account.