With the gallery thumbnails below the main image, the Retail theme simply defaults to the standard WooCommerce zero margins/padding for this.
To add some spacing between the main image and the gallery, add this CSS to Customize > Additional CSS:
.woocommerce div.product div.images .flex-control-thumbs {
margin-top: 30px;
}30px is 30 pixels so feel free to amend this value to whatever you think looks best.