Did you mean that you want to update the post author with the selected practitioner when you updated the post? If so, I believe you can use the acf/save_post hook, get the selected practitioner and then use the wp_update_post() function to update the post author.
If that isn’t what you mean, could you please explain it to me in more detail? If you can share some screenshots of the issue, that would be great too!
I hope this helps 🙂
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