Doing this will be fairly complicated. I do not know of any examples for doing this exactly but there are some examples of other cases available of the web if you do a google search for acf populate seclect field based on another field
I can give you a rough outline of what you need to do.
The first step will be to use an acf/prepare_field filter to dynamically populate the choices for the second select field based on the first field. This is necessary so that if there is a currently selected value that this value is include in the available choices. Without this step the selected choice will be un-selected when the page is reloaded.
The second thing you will need to do is add custom JavaScript to ACF. Your script will need to have a action that fires when the first field is changed and update the available options in the second field.
