This is what it says. Take note of the text that I made bold.
- Wait for an animation to appear on your new device. Hold your current device over the new device, then center the animation in the viewfinder. Wait for a message that says Finish on New [Device]. If you can't use your current device's camera, tap Authenticate Manually, then follow the steps that appear.
IOW, imagine taking a photo of the animation on the new phone with the camera on your old phone, but you don’t actually take the photo. You just get the animation centered in the viewfinder and that should trigger the action.