Once you have started AR 3S access the "Main" menu and click on "Realign Origin".
A red square with the hologram of a QR code next to it will appear. This mode can be exited by performing the Air Tap gesture anywhere in the air.
Scan your QR code as soon as you are prompted to do so by by lowering your gaze at the QR code so that it is enclosed by the red rectangle.
Two holographic green lines will run across the QR code and a scanning sound is emitted. A window will pop up reading "Shall Position and orientation of this reference be applied to the App Origin?".