The elements he is referencing here are actually color - LIGHT.
Their true nature of these 5 elements are the five-color lights: Blue, Green, Red, White and Yellow.
The Special techniques used to cultivate and attain the Rainbow Body are known are Tregcho and Thodgal.
The two practices belong to the Dzogchen Upadesha series of teachings, they are considered a top spiritual secret and should only be practiced under the guidance of a competent Dzogchen Master or Guru.
Book Sources:
Wild Awakening: The Heart of Mahamudra and Dzogchen:
https://docdro.id/FNyHV7c
The Supreme Siddhi of Mahamudra - Sean Price:
https://docdro.id/orMjFXM
The Bodhisattva Vow (Dzogchen Ponlop Rinpoche)
https://docdro.id/hekRc3g
Science of Magic and Magnetism Lesson #1
Charging through Energy Cultivation Part 1
Charging through Energy Cultivation Part 2