View file Uhost/UHOST_PACKAGE/WHMCS_THEME/uhost/store/not-found.tpl

 <div class="panel panel-default col-md-4 col-md-offset-4">
    <div class="panel-body text-center margin-bottom">
        <h2>
            <i class="far fa-times fa-2x text-danger"></i><br>
            {lang key='store.addon.notFound.productUnavailable'}
        </h2>

        <p>{lang key='store.addon.notFound.productUnavailableText'}</p>

        <p><em>{lang key='store.addon.notFound.ref'}: {$productName}</em></p>

        <a href="{$WEB_ROOT}/contact.php" class="btn btn-default">
            {lang key='store.addon.notFound.contactSupport'}
        </a>
    </div>
</div>
<div class="clearfix"></div>