Add a Thumbnail to Group Product in Woocommerce

Hello,

I am trying to display Thumbnails next to each of my products on my main group product page.

I saw this post :https://stackoverflow.com/questions/29033832/add-a-thumbnail-to-group-product-image-in-woocommerce

Which gives a code how to do that. But it doesn’t work on my website.

Maybe someone knows how to do that ?

Thanks