See the following from Add and use passes in Wallet on iPhone - Apple Support
Add a pass
You may be asked to add a pass within an app after you perform an action such as purchasing a ticket. Or, you can tap Add to Apple Wallet when you see it from the following:
- Wallet-enabled apps
- Mail or Messages
- Web browser such as Safari
- AirDrop sharing
- Wallet notification after you use Apple Pay at a supported merchant
- QR code or barcode
- To scan the code, open the Camera app , then position iPhone so that the code appears on the screen.
Also see the following for other types of cards: Keep cards and passes in Wallet on iPhone - Apple Support