Hello Maryuningsih88
No, it is not possible to change the seat numbers. SBB has currently no possibility to select the seat numbers on a plan.
You can try to import the ticket in the Trenitalia app and choose another seat, but:
— If you make a exchange in the Trenitalia app, tickets are no more refundable.
— I don’t know if an exchange is possible for the same train or only for another train.
— Seat plans are not always available.
Kind regards
Danhiel