There is no option To add Boarding Passes in the Wallet app. This is because boarding passes are not added directly from the Wallet app like credit/debit cards are.
Boarding passes are added from the Airline’s app that you have installed on your iPhone. For example, if you are flying American Airlines, then you would open the American Airlines app and then check-in and receive a boarding pass in the app. You will also be given an option to add the boarding pass to the Wallet app by that app.
NOTE: Most Airlines will not let a passenger check in and get a boarding pass if there are more than 24 hours remaining to flight time.
Axel F.