The settings for variable products show in WooCommerce product edit screen, these settings allow you to add variations for each product in your online store.
The Schema for WooCommerce extension extend variable products and allow you to add more details for each product variation to be used in schema.org markup output.
Variable products are a product type in WooCommerce that lets you offer a set of variations on a product, with control over prices, stock, image and more for each variation. They can be used for a product like a shirt, where you can offer a large, medium and small and in different colors.WooCommerce: Variable Product
The problem with Product Variations in WooCommerce is that it’s missing few fields required by Google Merchant.
These missing fields trigger errors and warnings in Google Rich Results testing tool as well as in Google Search Console.
The Schema for WooCommerce extension allow you to cover these missing property fields by setting default values, which will be used if no property value defined in product variation data.
See screenshot below: (click to enlarge)
WooCommerce > Poduct > Variable Product > Variations