Custom code for products Shopify

How do I refer to an element within the product list on funnelish?

I have variants listed within each product for the product list. I need to refer to the variant (extract) the value of the selected variant and pass this to Shopify as an order.

Essentially have a x1, x2 and x3 bundle. With 3 different sizes. The x1 I can map the product to Shopify to process orders. The x2 and x3 I can’t because they can pick size of each one.

Any solutions highly appreciated