Hello @AnWo
Thank you for your inquiry.
The Swiss Travel Pass Flex (3 days in one month, in this case) gives you the right to travel on 3 freely selectable days within one month. Here are the details: Swiss Travel Pass – the All-in-one-Ticket for Switzerland | SBB
For any further question, please contact our SBB Contact Center (0848 44 66 88, CHF 0.08/min).
I wish you a nice day and a great time in Switzerland.
Greetings
EleonoraS