How can I list only Subcategories in Woocommerce

You can try this.

$args = array(
     'parent' => 100, // id of the direct parent
     'hide_empty' => false,
);

$cats = get_terms( 'product_cat', $args );

foreach( $cats as $cat ) {
  // do your loop stuff here
}

Here is more information on this function and additional arguments you can use.