I read that a devotee named Cholkar was initially very arrogant and argumentative. How did Sai Baba's guidance change him and lead to him being chosen to write the stories?

While the provided source text does not mention anyone named Cholkar, it does describe the author of the "Sai Leela" book, who was later named Hemadpant. According to Chapter 2, this author was indeed initially characterized as being "mischievous, talkative, cynical, and critical." He was proud of his wisdom, had a logic-driven mind, and was prone to argumentation. It was Sai Baba's inspiration that set him on the path to writing the stories. Sai Baba instructed him to avoid argumentation and dualistic explanations, emphasizing that where there is a mind for argumentation, there is an abundance of ignorance and Maya. The author's transformation began with this task, which required him to dissolve his ego.