Danhiel Iustina It is not possible, but this is not a problem. If a reserved seat is unoccupied 15 minutes after the departure, it can be used by another passenger.
RolandP Hello Iustina Is it for an international connection or a connection within Switzerland? Kind regards, Roland
RolandP Hello Iustina It is not necessary to cancel the seat for a national journey. Seat reservations on national services are not very common. Kind regards, Roland
Iustina RolandP i called at SBB and they cancelled it. Indeed, only by calling them you can cancel it.