Spoilers for the end of the movie:
At an early scene of the movie, we see that the demon Valak reveals his name to Lorraine and that the latter scribbles his name in her bible. Later, she hears the riddle from old Bill, where she realizes that if they knew the demon's name, they would have power over him, which they do -> that's how they beat him.
But I don't understand. Why would the demon reveal his name, since it was the only way to be defeated?
The demon wasn't the one telling Lorraine the demon's name. Lorraine's gift comes from God, which allows her to receive visions of demonic activity. The visions were one of the ways that God communicates with her, but it seems that God also was communicating with her subconsciously. Ergo, arranging certain objects to spell Valak's name.
The importance of seeing the name of the bracelet that the daughter is making is that it implies that the daughter has the same gift as her mother.
It could be argued that another spiritual being was helping guide Lorraine in her visions in order to learn the demons name. Lorraine has never just felt dark and evil connections so it could be the better side without fully interfering.
Adding on the answers given above we see another instance where there is external help to Lorraine. The alphabets are arranged in a manner where the name of the demon is clearly apparent. However, it hasn't been stated in the conjuring universe that some external being is actually helping Lorraine or are these just revelations because of her psychic abilities.
The entire "Conjuring Universe" is presented from an extremely religious view-point, start to finish, so the suggestion of the plot seems to be that Lorraine gets her abilities from the Christian god, and she is able to figure out the demon's name because of her abilities, not because the demon told her.
