I went through the questions, but I didn't find an answer to this kind of sentence. Would you tell me what would be the correct sentence A or B? I had 2 beta readers and 2 answers. Thank you.
A) It was one of those last beautiful days of an Indian Summer, and the universe — or fate, you decide what to call it — had other plans for her.
B) It was one of those last beautiful days of an Indian Summer, and the universe — or fate, you decide how to call it — had other plans for her.
First, the direct answer to your question:
... and the universe — or fate, you decide what to call it ... (correct)
is the correct way to say this.
... and the universe — or fate, you decide how to call it ... (incorrect)
is not grammatically correct.
In English, the phrase "how to <do something>" is often explained as meaning something like "in what way", but more specifically, it almost always means more along the lines of "by what process or procedure".
As such, saying "how to call it", actually means "by what procedure you call it", which particularly in the case of the verb "call", usually means something substantially different:
Q: Do you know what to call that animal?
A: Yes, that is called an "emu".
whereas:
Q: Do you know how to call that animal?
A: No, I'm afraid I have no idea how to get it to come over here.
