Your Eurail one country pass Italy will not cover the travel within Switzerland. You will need to buy a normal ticket to the Swiss/Italian border station, most likely Domodossola. 

Or Chiasso.

Do note that normal railfares in Swiss are very, extremely high-the local planner will give 50%-as they aim the normal Swiss who holds a half-fare discount card! On SOME=not all connections you can et a lower price by booking fixed in advance.

@Jimmylin 
If you want to travel between Italy and Switzerland the best option would be the Eurail Global Pass, although it is a little more expensive, both countries are included. There is also the option of the Eurail Pass One Country - Italy, however this Pass only covers travel in Italy and to cross to Switzerland, you will have to take a train to the border and then buy point to point tickets for travel within Switzerland.

I just wanna add that Trenitalia (Italian Rail) offer a own pass Tenitaliapass this pass covers even the reservations of the trains. 

With Eurail and Interrail you have to pay on sometrains ontop for reservations in  case of Italy usually 10€