Hi Hidieh:
You can use the id parameter (one of the arguments passed to acf_form) to create a unique id for each of your forms. In your function triggered by the submit form action then use the global for acf_form to retrieve the ID value ($GLOBALS[‘acf_form’]).
See Elliot’s responses in this thread (though the original question is different from what you are asking) for more detail:
https://support.advancedcustomfields.com/forums/topic/acf_form-id-not-being-set-from-args/
Hope this is helpful!
