Place the mirror appoximately 2 meters from the I-pad camera lens.  (There is a string attached to the mirror that will allow you to easily start with the proper 2 meter distance).  You can carefully move the I-pad back and forth so that the mirror image completely fill the camera lens aperture.  Set the I-pad to maximum zoom, focus, and then adjust the brightness until the image on the mirror shows good index of refraction phenomenon.  The simplest way to get this adjustment right is to put a cup of hot water in front of the mirror and the adjust for maximum contrast.  Hot water, your hand, a lit match, a lit grill lighter, an unlit grill lighter showing the gas discharge, ice cubes, a bit of CO2, your breath, will all show very good Schlieren effects.