How to Hide the "Sticky Header 2020" Admin Menu

function plt_hide_sticky_header_2020_menus() {
	//Hide the "Settings → Sticky Header 2020" menu.
	remove_submenu_page('options-general.php', 'sh2020-settings');
}

add_action('admin_menu', 'plt_hide_sticky_header_2020_menus', 11);

Where do I put this code?