How to Hide the "emfluence Marketing Platform" Admin Menu

function plt_hide_wp_emfluence_menus() {
	//Hide the "Settings → emfluence Marketing Platform" menu.
	remove_submenu_page('options-general.php', 'emfluence_emailer');
}

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

Where do I put this code?