If you already have properly prepared products with the appropriate adaptation of variants, the plug-in is switched on automatically. All you have to do is in the WooCommerce> Switcher of variants tab, enter the names of the fields you want to exclude from the changes. This is recommended for variants of the size type. Because then we have many sizes assigned to one picture. And for example, only one picture is used for the color.
We disable the size on the example store. As you can see below:
If you do not know how to set up products, please visit this page: How to set a product with variants?.