I think you can read this Joomla documentation here https://docs.joomla.org/J3.x:Two_Factor_Authentication (copy the whole link before you access the link) .

What we do is just render the "Two-Factor Authentication" input field from the login form and display the "Two-Factor Authentication" field on the edit profile page so that the user can decide whether they want to activate this Two-Factor Authentication for their account or not.