Get related product based on subcategory selected from category id with ID 142

you can use this code or adapted to work for you case,, hope its work.. Add it to your function.php

add_filter( 'woocommerce_product_related_posts', 'woocommerce_get_direct_related_products' );

function woocommerce_get_direct_related_products() {
    global $woocommerce, $product;

    // Related products are found from category
    $cats_array = array(0);

    // Get categories
    $terms = wp_get_post_terms( $product->id, 'product_cat' );

    //Select only the category which doesn't have any children
    foreach ( $terms as $term ) {
        $children = get_term_children( $term->term_id, 'product_cat' );
        if ( !sizeof( $children ) )
            $cats_array[] = $term->term_id;
    }

    // Don't bother if none are set
    if ( sizeof( $cats_array ) == 1 ) return array();

    // Meta query
    $meta_query = array();
    $meta_query[] = $woocommerce->query->visibility_meta_query();
    $meta_query[] = $woocommerce->query->stock_status_meta_query();

    $limit = 5;

    // Get the posts
    return array(
        'orderby'       => 'rand',
        'posts_per_page'=> $limit,
        'post_type'     => 'product',
        'fields'        => 'ids',
        'meta_query'    => $meta_query,
        'tax_query'     => array(
            array(
                'taxonomy'  => 'product_cat',
                'field'     => 'id',
                'terms'     => $cats_array
            )
        )
    );
}