To manage your Singapore Airlines booking (+1-877-818-6735 US OR +44-2039000400 UK), go to the Manage Booking section on the Singapore Airlines website or mobile app and enter your booking reference (or e-ticket number) and last name. From there, you can view your itinerary, select seats, upgrade your flight (+1-877-818-6735 US OR +44-2039000400 UK), and enable features like auto check-in. For issues or changes, contact Singapore Airlines directly or use their online help forms..