Hi, I have solved this problem adding this code in functions.php:
add_action( 'woocommerce_single_product_summary', 'woocommerce_template_top_category_desc', 1 );
function woocommerce_template_top_category_desc (){
$terms = get_the_terms( $post->ID, 'wc-attibute-class' );
if ( !empty($terms)) {
$term = array_pop($terms);
$text= get_field('txt-field', $term);
if (!empty($text)) {
echo $text;
}
}
}