If you wish to remove or add bags and seats from your itinerary, you can do it during the time of advance check-in just move to the allegiant.com and navigate to the 'Manage Trip' tab displaying on the page. Input all your itinerary details like confirmation number, first name and last name in the spaces and hit the 'Continue.' You can also change your seats and add bags during advance check-in (on the Allegiant website or the Allegiant mobile application).