Good news I was looking to add a button to the admin metabox created by ACF to pass an ajax action and found a great solution for you here.
https://github.com/SnakeO/acf-admin-button-field
This code will allow you to add a plug-in that adds a ‘button’ to your field types and there you can set it for external URL or AJAX – the rest is like every other AJAX solution that is well documented around the web.
Hope this helps you. I’ve already used it for my project. It worked great!
