Tap the Lens icon.

It’s the camera lens icon that you’ll see to the left of the trashcan icon at the bottom of your screen. You’ll see the QR details slide up from the bottom of the screen.

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How do I scan a QR code on my iPhone with camera roll?

Open the Camera app from the Home Screen, Control Center, or Lock Screen. Select the rear facing camera. Hold your device so that the QR code appears in the viewfinder in the Camera app. Your device recognizes the QR code and shows a notification.