Hello Queackooto27
You are not having the SwissPass but the Swiss Travel Pass. This is not the same, and you may confuse train staff if you use the wrong term.
Log in the app using the same credentials as for the website. It should appear under tickets, if not, pull down the screen in the centre of the app, to refresh the tickets list.
There is no need to have a ticket to book seats. To book a seat reservation is a separate task if needed at all. No one checks if you have a ticket upon booking of a seat. Checking your seat reservation and the ticket is the sole task of the ticket inspector.
Kind regards,
Roland