Hi Ronald, and welcome to MySwissAlps!
>> We are planning to go from Zermatt to Locarno via train in September. In some of the information , it seems that the Italian portion of the trip recommends a reservation but I haven't been able to figure out how to do this.
Do you mean the Centovalli Express between Domodossola and Locarno?
Reservations are possible on most, but not all, Centovalli departures, and can be made on the Centovalli website at a cost of 4,00 or 5,50 Euro.
Here is the link, and I have included some vocabulary to assist you in completing the transaction. The instructions below assume you are travelling with a Swiss Travel Pass:
Change the language to English if necessary, on the top right of the page.
- Travel document - choose Turistico
- Progressivo biglietto - in this field, put Swiss Travel Pass
- The default is a return journey, so change it to single
The rest should be easy enough to follow.
At the end, what you get is a prenotazione internazionale - international reservation.
If you wanted to, instead of getting a train through the Simplon tunnel between Brig and Domodossola, you could get the Swiss PostBus #631 over the Simplon Pass from Brig to Domodossola instead. The bus drops you very close to the station at Domodossola, from where you can catch the Centovalli Express for the rest of the trip to Locarno.
It is a very scenic trip through the mountains. If you are interested, you can read my trip report about it under the heading Saas-Fee to Locarno on the following page:
>> Is a reservation really necessary and if so - how do we do that in advance?
I travelled from Domodossola to Locarno on the Centovalli Express in September 2016 and didn't reserve. (Actually, reservations were not possible at that time - they are a more recent introduction.) Although the train was well patronised, I found a window seat OK. However, it doesn't cost much to reserve, and you can ensure that you sit together and get a window seat, so it's probably worth it. Personal choice in the end :)