The key to the Sixth Layer of Fire Life lies in first finding where one's Life Fire resides within. This Life Fire is deeply hidden at the junction between the body and the soul, extremely difficult to locate. If one cannot even find it, then there is no talking about strengthening or changing its burning frequency.
Next, what he needed to do was to successfully locate the Life Fire once. Compared to other cultivators, he only needed to succeed once, no matter how arduous, hard to find, or hard to grasp, he just needed one success.
After that, he could easily repeat this successful process continuously and without end.