How can I remove a WooCommerce Product Tab’s sub section in wp-admin?

To change this “sub navigation” you could use the WooCommerce filter “woocommerce_get_sections_products“.

The following example code will remove the sub navigation point “inventory”:

function change_navi_function($sections)
{
    // remove sub navigation point "inventory"
    unset($sections['inventory']);

    return $sections;
}

add_filter('woocommerce_get_sections_products', 'change_navi_function');

What you have to do now is either to hook your “change_navi_function” function after the function from the premium plugin and then remove the “Product Vendors” from the “$sections” array. Or you unhook the function from the premium plugin which use the “woocommerce_get_sections_products” filter.