Three coins count as six, how to determine which side is yin? Which side is the sun?

I have seen Mr. Zhang Jialin's speech. Mr. Zhang is a scholar who has studied the Book of Changes for many years. In the program, he taught a large family to calculate divination with coins, and both yin and yang decided for themselves, because the probability of occurrence was equal. In ancient times, it was also decided to calculate divination with copper coins. But before divination, you need to determine which side is yin and which side is yang.