This is Elias with Shopify Support. Thank you for reaching out.
I understand you're looking for help with pasting the code for Product Review into your theme's coding. There's a step-by-step guide for using the Product Reviews app, which can help walk you through installing the app's coding on sectioned or non-sectioned themes. If you're using a Shopify-supported theme, then our Support would also be happy to assist you with this through live chat, email, or callback. To create a support request, please visit the Shopify Help Center and log in to your account.
That being said, if you're not using a free theme from Shopify, then your theme was made by a third-party developer. For third-party or custom themes, you can always contact the theme developer and see if this is something they can help with. However, if the theme developer isn't able to help with customizing your theme, then you can consider hiring a developer from Shopify Experts as well. Shopify Experts are experienced in working with third-party and custom themes, and they'll be able to create a solution for your store.
I hope this points you in the right direction to get help with Product Reviews. If you have any other questions, please don't hesitate to let me know!