You could go to the SBB Travel Center upon arrival to have it corrected.
However, working as a ticket inspector, I can tell you, this is a very common mistake by people from the american continent; it is not an issue as the error is so obvious and all personal data given on the Swiss Half Fare Card is still matching the data in the passport. It would be a different story if the date of birth was completely different or, due to the wrong month, a 16 years old passenger would take advantage of reduced fares because they were still considered as 15 years old by the ticketing system (child fares from 6 to 16 years of age).
Your bad luck, you were both born on a day that also exists as a month, otherwise the system would have rejected the month entry 🙂
My advice, when buying e-tickets, simply enter the same (wrong) date as you entered for the Swiss Half Fare Card. By doing so, during ticket check, when both, the Swiss Half Fare Card and the ticket are scanned, the ticket control device will not throw an error message due to inconsistency.
Simply have your passport physically (no copies) with you when ever you travel with e-tickets.