There are several ways to add boarding passes to your Apple Wallet:

  1. Scan your boarding pass into the app: Boarding Pass widget > Attach > Scan boarding pass.
  2. Go to manual check-in (boarding pass widget → check-in → check-in manually) > go through the check-in process to the screen where you see Bar code with your boarding pass > make a snapshot > if the flight is recognized, you will have the option to add the boarding pass

And now you can add your boarding pass into Apple Wallet. Here is a visual: