My son borned on 19/1, he only able to do it few days ago after the training / assistance I provided.
What I did :
I slowing turn him from facing up to facing down by turning his leg and arm. As he don't like facing down, he tried to follow what I did by turning his leg and arm. After several attempts, he is able to do it. Very amazing
When the baby 反到一半, you may assist him / her by pushing him / her a bit. They are smart. They will be able to do it shortly.
Hope to hear the good news from you.