Hi Pooh
Thank you for your request.
Saver Day Passes that you purchase in the SBB Mobile app or on SBB.ch while logged in can be refunded/exchanged free of charge within 30 minutes of the time of purchase. Once those 30 minutes have elapsed, only in exceptional cases.
You can find all the information here (under Exchange/refund).
I wish you a good Sunday.
Best regards
NicolasK