How to add a QR code to Apple Wallet? "Edit Passes" button in mentioned in Apple Guide does not exist

A QR code just encodes a small block of data. It is quite possible that you cannot add any old QR code to Apple Wallet - that when you “add a QR code” it needs to be from an issuer who supports the Add to Apple Wallet feature.

Edit passes will only allow you to delete those passes already added. Unless your ticket provider has enabled "add to wallet" functionality, you will be unable to add your ticket to the wallet. Take a picture of the QR code or use the email on your device.

Adding Boarding Passes, Bookmyshow Tickets, IRCTC (Railway) tickets, Airline Tickets, Game Tickets and Hotel Bookings are only possible if the issuer has enabled the "Add to Apple Wallet" feature for the tickets/passes issued by them. See some examples below.

The card issuer must enable the "Add to Apple Wallet" feature.

You will find this in the Card Issue Document

1. Tap Add to Apple Wallet.
2. 

FWIW I just had this problem with an email ticket for a cinema. I couldn't find any wallet option on the popup menus from the QR code image in the email.

Solved it by going to the bottom of the email and finding a download link - that took it straight into the wallet.

YMMV it probably depends on the how the company crafted it's email.

pass4wallet does just this: take a barcode or a qr code and put it into the apple wallet. You can even choose color and title of the card. Only problem so far is that the qr code is a bit small, some low quality qr code scanners struggle... But it s and iOS limitation it seems.

https://apps.apple.com/us/app/pass4wallet-store-cards/id1423106610

Why not just save the e-mail? Then when you need to present the QR code to the ticket taker, bring up the e-mail.