Go to “Product Listing” page and select any product you want to link with the existing Shopee product and click Action > Edit Shopee Product.
Enter your Shopee product ID and save.
To get the Shopee product ID, you need to login to your Shopee Seller Centre and go to My Product page. Select any product and click More > Live Preview.
You can get the Shopee product ID in the URL of the page in the address bar. See screenshot below as an example.
After you get the Shopee product ID, fill in the Shopee ID and save.