The Shopify Lite/Starter plan does not give you access to your HTML files.
Using this Shopify plan? Follow this guide to install the Kudobuzz widget on your product pages.
1. From your Kudobuzz dashboard, click on Customize Widgets >>> Review Form Widget.
Copy the piece of code on the page.
2. Head over to your Shopify admin. Click on Products and select any of your products.
Click on the symbol <> and paste in the code.
3. In the address bar, copy the string of numbers at the end of the URL. This is your product id.
4. Replace "product.id" in the code with the product id you have copied.