Yes, you can still change your seat after you have checked in for an EasyJet flight, but you must do so through the "Manage Bookings" section of the website or the mobile app. Once you have already checked in and received a boarding pass, selecting a new seat will typically require you to pay a seat selection fee (unless you have a fare type that includes it). After you successfully change your seat and confirm the selection, the system will void your old boarding pass. It is critical that you check in again and download a new boarding pass reflecting your updated seat number. You can make these changes up until two hours before the scheduled departure time, provided there are still seats available on the aircraft.