I've already booked another fare seat, can I change it to JINI PLUS?

You can change the reservation (ticket reissue) to the Jini Plus if you pay the extra fare difference from the ticket you purchased. Or, you can purchase the jini Plus Seat at the airport on the same day after purchasing the ticket at a regular fare. However, please note that if there are no remaining Jini Plus seats left at the airport, the seats are not available.