How to Hide WebP Express Admin Menus

function plt_hide_webp_express_menus() {
	//Hide the "Media → WebP Express" menu.
	remove_submenu_page('upload.php', 'webp_express_conversion_page');
	//Hide the "Settings → WebP Express" menu.
	remove_submenu_page('options-general.php', 'webp_express_settings_page');
}

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

Where do I put this code?