You will need to use product slug or ID to import reviews for your WooCommerce products
Get WooCommerce product's slug
Login your WordPress admin > Products > All products

2. Hover on a product that you want to get slug, click on "Quick edit" then you can see Slug of product

Get WooCommerce product's ID
Login your WordPress admin > Products > All products

2. Hover on a product that you want to get product's ID then you can see ID of product

All the best,
Ryviu team.