If the email has been properly sent 23h before boarding, when the online check-in is open. In that email, a direct link to go to check-in online is given, and this link, if working properly, should directly log you in the check-in process. The online check-in should however load properly in most cases, both on desktop and on mobile versions of their website. The Lufthansa seat select is available from the online check-in main screen. Some seats will be assigned by default, and they can be changed – however, the closer to the departure time, the more the seats will already be taken. If a Lufthansa seat reservation has been done when booking the flight, the Lufthansa pick seats system should have already assigned them to the passenger. By clicking on the Lufthansa change seats option, flight after flight, it is possible to select the flight on the plane. Both the main traveler and the fellow travelers can be placed in the plane, and the seats without window or at the emergency exit are properly marked.