Yes, a Swiss Travel Pass can be exchanged, provided
- the exchange is done before the STP’s first day of validity
- It was bought with SBB
The exchange can be done by phone (+41 848 44 66 88) or at any SBB Travel Office.
However, I wondered if it makes sense to exchange your STP. Wouldn’t it be an option to buy a Saver Day Pass for day 5, or even a single ticket provided the amount to be spent does not exceed the average cost per day of a 6 days pass?
Should you have bought the STP with an agency, for example Klook, kindly seek advice with them concerning an exchange.