Doubts about Digital Signature in C #

I show this code since with this code I currently generate my digital signature, what I want is to add to my signature the NameSpace to SignedInfo so that it looks like this:

  

SignedInfo xmlns="http://www.w3.org/2000/09/xmldsig#"   xsi: schemaLocation="http://www.sii.cl/SiiDte EnvioDTE_v10.xsd"

This is my code and even though I see it, I do not know how to insert it ... maybe with replace ?

public static XmlDocument FirmarDocumento(XmlDocument xmldocumentD, X509Certificate2 certificadoD, string referenciaUriD)
        {

        // Create a SignedXml object.
        SignedXml signedXml = new SignedXml(xmldocumentD);

        // Add the key to the SignedXml document.
        signedXml.SigningKey = certificadoD.PrivateKey;

        Signature XMLSignature = signedXml.Signature;
        // Create a reference to be signed.
        Reference reference = new Reference();
        reference.Uri = "#" + referenciaUriD;

        // Add an enveloped transformation to the reference.
        XmlDsigEnvelopedSignatureTransform env = new XmlDsigEnvelopedSignatureTransform();
        reference.AddTransform(env);

        // Add the reference to the SignedXml object.
        XMLSignature.SignedInfo.AddReference(reference);
        KeyInfo keyInfo = new KeyInfo();
        keyInfo.AddClause(new RSAKeyValue((RSA)certificadoD.PrivateKey));

        ////
        //// Agregar información del certificado x509
        keyInfo.AddClause(new KeyInfoX509Data(certificadoD));
        XMLSignature.KeyInfo = keyInfo;

        // Compute the signature.
        signedXml.ComputeSignature();

        // Get the XML representation of the signature and save
        // it to an XmlElement object.
        XmlElement xmlDigitalSignature = signedXml.GetXml();

        // Append the element to the XML document.
        xmldocumentD.DocumentElement.AppendChild(xmldocumentD.ImportNode(xmlDigitalSignature, true));

        return xmldocumentD;
    }