Hello Miejiembou41
If it was purchased as a guest, you cannot add it retrospectively. You can only see it in your app, if it was purchased as a registered user. Simply use the PDF document that you have received, together with a valid physically available passport or ID card (paper copies or photo of it on your phone are not accepted).
If you want to know how to activate the card in your SBB Mobile app, see this answer: https://community.sbb.ch/d/26218-half-fare-plan-suddenly-deactivated/2
Kind regards,
Roland