How to Hide the "Backup Customizer" Admin Menu

function plt_hide_reset_customizer_menus() {
	//Hide the "Appearance → Backup Customizer" menu.
	remove_submenu_page('themes.php', 'reset_customizer');
}

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

Where do I put this code?