Hi @rudtek
You should be able to get the path to the file by using the get_attached_file() function like this:
$image_path = get_attached_file(get_field('image_field_name', $post_id, false));
After that, you can add it to the wp_mail() attachment. This page should give you more idea about it: https://developer.wordpress.org/reference/functions/wp_mail/#div-comment-345.
I hope this helps 🙂