Hello Fehaunue14
In Switzerland, a ticket never guarantees a seat as our trains are all free seating except for the Glacier Express (GEX) and the Golden Pass Express (GPX) which both need a mandatory seat reservation in addition.
A ticket only grants transportation from your desired point of departure to the desired point of arrival, yet not the seat. And for some trains, you cannot even reserve seats. You can read more about seat reservations in our blog:
https://community.sbb-tickets.cc/blog/23887-demystifying-seat-reservations-on-swiss-trains-a-comprehensive-guide
Holding the Saver Day Pass, you simply hop on and off the public transport services at will. If there is no seat left, you might have to stand or take the next service. However, with a 1st class ticket you will always find a seat.
To reserve your seat for Glacier Express, see this website:
https://www.glacierexpress.ch/en/
Kind regards,
Roland