Found an answer:
To request a refund for your tickets bought on SBB.ch due to the cancellation of the EC178 train, please follow these steps:
Refund Request Form: Fill out the refund request form available here.
Form Selection: Choose “A ticket / travelcard / other products” and then “International ticket” in the form.
Required Information: You will need to provide the following details:
Order number
A brief description of the case
Your personal IBAN number
Name of your bank
BIC/SWIFT code of your bank
The PDF ticket for your order
Deadline: Refunds will only be accepted up to 1 month after the train’s scheduled departure.