Use the set/reset button to remove the Google secret keys stored and set a new one and to start using Google Authenticator codes for two- factor authentication. This can also be done using the Reset password but this would reset all the 2FA mechanisms.
On pressing the reset button, the new QR Codes would be displayed. Make sure that the Google Authenticator app is installed on your phone. Use a suitable QR reader to scan the secret number or manually note down the secret.
If User does not have any 2FA mechanisms set, then the user would be prompted to to complete the setup on first time login into the webpanel.
Once this is setup, user would be prompted to enter the codes to login. In the event of loosing your phone, this would have to be reset by another user with admin privileges via web interface.
Use the Google Authenticator which needs to be installed on your phone. Use it scan the QR codes and use it start generating the codes.