How to Hide NS Custom Placeholder Image For Woocommerce Admin Menus

function plt_hide_ns_custom_placeholder_image_for_woocommerce_menus() {
	//Hide the "Placeholder" menu.
	remove_menu_page('ns-custom-placeholder-image-for-woocommerce/ns-admin-options/ns_admin_option_dashboard.php');
	//Hide the "Placeholder → Placeholder" menu.
	remove_submenu_page('ns-custom-placeholder-image-for-woocommerce/ns-admin-options/ns_admin_option_dashboard.php', 'ns-custom-placeholder-image-for-woocommerce/ns-admin-options/ns_admin_option_dashboard.php');
	//Hide the "Placeholder → How to install premium version" menu.
	remove_submenu_page('ns-custom-placeholder-image-for-woocommerce/ns-admin-options/ns_admin_option_dashboard.php', 'how-to-install-premium-version');
}

add_action('admin_menu', 'plt_hide_ns_custom_placeholder_image_for_woocommerce_menus', 11);

Where do I put this code?