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https://docs.woocommerce.com/document/woocommerce-display-category-image-on-category-archive/

Select a new Image in Thumbnails and place the code below to where you want to 
show that image

<?php

global $wp_query;
$cat = $wp_query->get_queried_object();
$thumbnail_id = get_woocommerce_term_meta( $cat->term_id, 'thumbnail_id', true );
$image = wp_get_attachment_url( $thumbnail_id );
if ( $image ) {
  echo '<img src="' . $image . '" alt="' . $cat->name . '" />';
}