I purchased 2nd class Swiss Travel Pass, but my seat reservation of Glacier Express is 1st class. I would like to upgrade the class for this. The SBB App shows seat is not available and can’t purchase the upgrade. How can I process the upgrade before departure? Also, I heard that the class upgrade with Swiss Travel Pass is to pay the half of the price difference between 1st class and 2nd class. But, I didn’t see this. Is that information correct?