First of all you have to go to the Metro Link plus startpage. For Germany this would be https://de.metrolink-plus.com/ 

On this page on the top right you will find the 'Login' link.

Behind this login link you will find the login page consisting of 'User name' and 'Password' field.

The 'User name' is equal to the mail address you have been registered with.

The 'Password' is the one you have set during the registration. If you forgot your password please use the link below the login fields to set a new one.

If you have entered 'User name' and 'Password' correctly you will be routed to the next page for entering the so called 2nd factor. This is a 6-digit code you either receive by SMS or get through the Authenticator app depending on the choice you have made during the first login after the registration.

After that you are in the Metro Link plus portal.