Hello DanielChang85,
The SwissTravel Pass is only valid in Switzerland.
You have to buy a reservation and a ticket for the italian part.
To buy this ticket, you can call our Railservice (a credit card is required): 0900 300 300 (1.19/Min). My colleagues will call you back, so that you didn't pay the phone costs. You can also go to a SBB counter.
I wish you a pleasant day.
Kind Regards,
CharlineB