Can you recommend any reading material that explains the process?
There are several books and academic papers which describe the origins and theoretical underpinnings of Brainspotting therapy and Somatic Experiencing® trauma renegotation. The seminal texts were written by Dr. David Grand and by Dr. Peter Levine. Most people find these books excellent starting points.
Grand, D. (2013). Brainspotting: The Revolutionary New Therapy for Rapid and Effective Change. Boulder, CO: Sounds True.
Levine, P. A. and Frederick, A., (1997). Waking the Tiger: Healing Trauma: The Innate Capacity to Transform Overwhelming Experiences. Berkeley, CA: North Atlantic Books.
A full booklist (not exhaustive) on body-oriented healing and academic papers referring to the Somatic Experiencing® can be found on the Resources page of this website.