As of v4.0.1, WooCommerce does not provide a filter to change the output of related products without also affecting the products everywhere else.
To customize the HTML markup of related products, we need to place a copy of woocommerce/templates/single-product/related.php in the child theme under woocommerce/single-product/related.php and make the necessary changes.
If you do not want to or can not use a theme like in the case of Oxygen, you have to use a custom functionality plugin for this.
In this premium members-only article I share a plugin named WPDevDesign - Custom Related Products that you can use as an example and further modify for outputting custom HTML markup for WooCommerce related products on single product pages.
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