In fact, while An Jing was cultivating, Chenyinzi did provide some help.
But it was precisely because of this that he found it unbelievable.
The formation of the Bright Mirror Heart required some intricate tricks that couldn't be taught by scriptures alone, and the experiences brought by Mingguang Dust's own embodiment also carried his strong personal characteristics; An Jing's meridian operation was different from his, and could not be completely applied.
In this respect, Chenyinzi explained many principles of the Bright Mirror Heart to An Jing, such as how it stably gathers spiritual power by contracting and expanding, continuously refining and storing it in great detail.