Imade a first class reservation on the Glacier Express. This is a mistake because I intend to purchase a second class Swiss Pass. What should I do? Could I change my reservation to second class on Glacier Express?
Changing the reservation means cancelling the current one and getting a new one. Whether that's possible and if costs are involved needs to be checked with the company you purchased from.
Another option is to enjoy the Glacier Express in 1st class. An upgrade ticket can be purchased at the rail station in Switzerland and costs CHF 56.50 per adult.