Add acf field to woocommerce product via functions file
/*Add ACF Fields for Woocommerce Product Single*/
add_action( 'woocommerce_before_add_to_cart_form', 'display_acf_field_under_description', 30 );
function display_acf_field_under_description() {
if( get_field('used_serial') ): echo '<b>Serial Number:</b> ' . get_field('used_serial'); endif;
}