There isn’t a lot of documentation or useful examples of doing what you want. I have created an example of how to do something similar to this, my example draws it’s information from post types, but it can be changed to other sources of information. The important part of the example is the JS code that gets the value from one field when it’s changed and hooks into the ACF ajax code to get the results to populate another select field with. Hope it helps https://github.com/Hube2/acf-dynamic-ajax-select-example/tree/master/dynamic-select-example
