To have the Swiss Travel Pass available in the app is only possible if you bought the Swiss Travel Pass from SBB as an authenticated customer. If you then log in to the app using the same credentials as for purchase, your STP will automatically appear in the app. Had you bought it as a guest or from a reseller, you cannot add it to the app at a later stage. You are welcome to store your PDF on your mobile device and to show it from there.
→ Kindly note, no matter how you present your Swiss Travel Pass, when travelling with a Swiss Travel Pass, you must always carry your passport physically with you and present it when asked to do so. Passport copies on mobile devices or photos of it are not accepted as proof of ID.
We wish you already now a pleasant stay in Switzerland.