I think you are referring to the Swiss Travel Pass, which is destined for tourists. The product was formerly named Swiss Pass yet has been renamed in 2014. The SwissPass is nowadays a product for residents.
Assuming you are holding a Swiss Travel Pass, I can tell that it is valid as far as Buchs SG. From there, you will need an international ticket to Slazburg. You can get it from www.sbb.ch/en. A seat reservation is optional.
Swiss Travel Pass – the All-in-one-Ticket for Switzerland | SBB