You should use this plugin to add snippets (otherwise you should create child theme and put code to functions.php).
Following plugins supported: Checkout Add-ons, PDF Product Vouchers, Woocommerce Subscriptions, WooCommerce Bookings, WooCommerce Appointments, WooCommerce Memberships, WooCommerce Product Vendors, Local Pickup Plus, FooEvents, Tickera, WooCommerce Box Office, Shipping Multiple Addresses, WooCommerce TM Extra Product Options (as column), WooCommerce TM Extra Product Options (as product rows)