Hello MichaelFletcher
Welcome to the SBB Community.
There is no app called SwissPass but SBB Mobile app. You probably meant the latter.
As a tourist, you do not have a customer number, only residents using annual and seaonsal travel cards do have it. Simply log in to you the SBB Mobile app using your e-mail and password. Then you are ready to use the app as a registered user.
Kind regards,
Roland