Hello Woophexeath67
You can either purchase
- a route-specific class upgrade, or
- a class upgrade for a day
both at half fare, whatever is cheaper depending on your travel plans for that day.
Go to this website
https://www.sbb.ch/en/tickets-offers/tickets/point-to-point-tickets-switzerland/class-upgrades-supersaver-class-upgrades/class-upgrade.html
and select the class upgrade you want to purchase (I guess the route-specific class upgrade is sufficient); then enter the passenger information and select “Half Fare Card” as reduction.
The class upgrade is an e-ticket which you simply present together with the 2nd class STP.
Please let us know if you need further advice. If you tell us from where to where you will ride the Glacier Express, we could provide you with a screenshot how to purchase.
Kind regards,
Roland