A few tips:
In the future, if your topic is a question, please do not mark it as a post. Can you please edit this topic and set it as a question so it can be marked solved once complete.
I would use the get_posts function which accepts the WP_Query args to find the posts. There are args that allow you to search for custom field values. There is even documentation on the ACF site that talks you through how to query posts based on custom field values.
On that note, did you not search before posting this question?
