newsupernova/vendor/magento/module-sales/view/frontend/templates/order/creditmemo.phtml

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
?>
<div class="order-details-items creditmemo">
    <?= $block->getChildHtml('creditmemo_items') ?>
    <div class="actions-toolbar">
        <div class="secondary">
            <a href="<?= /* @escapeNotVerified */ $block->getBackUrl() ?>" class="action back">
                <span><?= /* @escapeNotVerified */ $block->getBackTitle() ?></span>
            </a>
        </div>
    </div>
</div>