Hello Travelfish
It’s important to distingiush for these panoramic train between the ticket (affected by half fare) and the seat reservation (mandatory), which is not affected by the half fare. These two are not linked, you can reimburse the ticket and keep the reservation for both trains.
The tickets can be reimbursed and rebought at halfe fare unless they are saver’s or supersaver’s tickets.
Did you buy the tickets online while logged in? If so, you can simply reimburse them (there is a link to do so in the confiramtion e-mail.
If you bought them online without logging in, you can call the SBB Contact Center 0848 44 66 88 (0.08/min) from Switzerland or +41 51 225 78 56 from aborad.
If you bought them at a station (at a ticket machine or -office) then it is easiest to also have the reimbursement done there.