https://stackoverflow.com/questions/47308732/get-url-of-variation-image-thumbnails-in-woocommerce
<?php
// find out $variation_id, it's different from product_id
$variation = new WC_Product_Variation( $variation_id );
$image_tag = $variation->get_image();
// The below is the whole image tag including <img> and some classes that will help customize it.
echo $image_tag;