Hello Pagoobach18
International tickets cannot be changed by e-mail, you must call or see a ticket office.
To call, see this information for South Korea which I found on the web:
It looks like you came to the wrong conclusion.
The Swiss Travel Pass does not give free access to Gornergrat and Jungfraujoch. It is also neither valid in France nor in Italy. Also, in just 3 days, your itinerary is almost impossible do be done. You are wasting a lot of time on trains… Did you check the train timetables to go from one place to another, see: www.sbb.ch/en.
I suggest you are going to purchase the Swiss Half Fare Card. With it, you could travel for half of the costs, and the Swiss Family Card for the kids will be included as well. Kids do not travel for free, they must be in the possession of the Swiss Family Card.
Just an example: if you purchase the Swiss Travel Pass, which is 77 CHF / day, you will have to purchase on top another ticket of 75% of the regular cost to Jungfraujoch. The Swiss Travel Pass grants a reduction of 25% only. The Swiss Half Fare Card grants a 50% reduction.
I, personally, have the impression, you are in a rush. Firstly, finish your planning (base, what to do when), secondly choose the tickets. You should also not forget that the weather plays an important role in our country. What if you plan to go to Gornergrat, you pay a fortune in advance for the tickets, while the weather is bad, and you will not see anything?
Furthermore, to go from Zermatt to Jungfraujoch makes zero sense. You would rather stay in Zermatt and go for the Matterhorn Paradise. Or, you go to Grindelwald instead of Zermatt.
You may want to let us know where you plannned your hotels, so we can help to plan a 3-day itinerary. Definitely, in just three days, while two of them are travel days (arrival / departure), you will not have seen much of our country.
https://switzerlandtravelcentre.com/en/che/ticket/swiss-half-fare-card
Kind regards,
Roland