Siebel: Append child tag in XML

Hello,

I need help on below requirement:

I have XML document, and I have to just add one tag in that. Please suggest How I can add using WF:

XML:

<?xml version="1.0" encoding="UTF-8" ?>

.<SiebelMessage MessageId="1-8307PY" IntObjectName="ABC SR Response IO" MessageType="Integration Object" IntObjectFormat="Siebel Hierarchical">

..<BackOfficeResponse>

...<Response>

....<BackOfficeServiceRequest>

.....<SRNumber>1-5901262480</SRNumber>

.....<ListOfActivity />

....</BackOfficeServiceRequest>

...</Response>

..</BackOfficeResponse>

.</SiebelMessage>

I want to add Description tag, I have value WF, I want below XML:

<?xml version="1.0" encoding="UTF-8" ?>

.<SiebelMessage MessageId="1-8307PY" IntObjectName="ABC SR Response IO" MessageType="Integration Object" IntObjectFormat="Siebel Hierarchical">

..<BackOfficeResponse>

...<Description>HELLO</Description>

...<Response>

....<BackOfficeServiceRequest>

.....<SRNumber>1-5901262480</SRNumber>