How to Hide the "Call Now Button" Admin Menu

function plt_hide_call_now_button_menus() {
	//Hide the "Settings → Call Now Button" menu.
	remove_submenu_page('options-general.php', 'call-now-button');
}

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

Where do I put this code?