Provided your original tickets were issued by SBB, can find the refund policy here:
If you bought it from another provider, you have to reach out to them.
As I assess the situation, there is no refund possible as the flat tire was caused by a third-party provider and is therefore not the fault of the railway either.
My advice: check with your travel insurance or Uber for any a compensation.
The final decision on any refund lies with SBB provided you bought the ticket with SBB at all.