There aren’t any tutorials or a lot of documentation on doing exactly what you want. I used to have examples of doing this, but that was before the new JS API in ACF. All I can do is point you in the right direction.
This all needs to be done using JavaScript and the ACF JS API.
ACF JS API: https://www.advancedcustomfields.com/resources/javascript-api/
Best source of AJAX information for WP: https://codex.wordpress.org/AJAX_in_Plugins
This is one of my old examples, it will not work. ACF no longer has the acf.ajax object, so you need to do that yourself. Most of what I do for reading and setting fields can now be done using the ACF JS API.https://github.com/Hube2/acf-dynamic-ajax-select-example/tree/master/dynamic-fields-on-relationship
This is another example that works with ACF now, however, the only change I made to get this working was to do the AJAX request differently, while I left most of the rest the same. All of the getting and setting of fields could have been done using the ACF JS API, I just did not realize this at the time. This could be done much better using the API. https://github.com/Hube2/acf-dynamic-ajax-select-example/tree/master/dynamic-select-example
