Place the XLR8 over the area of involvement (AOI). The clinician may choose to (#2) laser over the nerve root (located using the myotome/dermatome chart) or the organ involved (using the Merrick chart).
The reason the vagus nerve is discussed by other speakers is actually for the "Parasympathetic Facilitation" and "Sympathetic Inhibition" effect on the nervous system.
XLR8 works great. But you may see additional benefits with GVL or EVRL.
If you want to learn muscle testing (or you already do AK type muscle testing not just ortho/neuro) the Advanced Laser Video has many of the "activation method protocols" of the Vagus and "Parasympathetic Facilitation" and "Sympathetic Inhibition" that cannot be written in this manual. It requires a video.
Also, pulses/Hz's to slow the brain down can be very beneficial as the body works as systems. So Delta waves, theta waves even low beta waves can help facilitate parasympathetic. Using the mentioned settings while tracing the pathway would make sense for general application but implementing the variety of "activation" methods will enhance the physiological response.