Got it guys.
Here’s for a flexible field on
ACF Pro 5.3.2.2
add_action('acf/input/admin_head', 'my_acf_admin_head');
function my_acf_admin_head() {
?>
<script type="text/javascript">
(function($) {
acf.add_action('ready', function(){
$('body').on('click', 'li.acf-fc-show-on-hover a.acf-icon.-minus.small', function( e ){
return confirm("Do you really want to delete this?");
});
});
})(jQuery);
</script>
<?php
}