function filter_woocommerce_cart_totals_coupon_html( $coupon_html, $coupon, $discount_amount_html ) {
    $coupon_html = $discount_amount_html . 'My url';

    return $coupon_html;
}
add_filter( 'woocommerce_cart_totals_coupon_html', 'filter_woocommerce_cart_totals_coupon_html', 10, 3 );