How can I Insert Variable into an XML document

We are trying to insert a variable called str Account Number into an XML document. Please, Can anyone help with what tool step to use after I do an XML Create Document toolstep? Below is the XML document and we are trying to insert the account number where it says AcctId.

<soapenv:Envelope xmlns:soapenv=“http://schemas.xmlsoap.org/soap/envelope/” soapenv:encodingStyle=“http://schemas.xmlsoap.org/soap/encoding/” xmlns:ns=“http://www.fhnc.com/emm/1”>
soapenv:Header
<wsse:Security xmlns:wsse=“http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd”>
wsse:UsernameToken
wsse:Usernamexxxxxx</wsse:Username>
wsse:Passwordxxxxxx</wsse:Password>
</wsse:UsernameToken>
</wsse:Security>
</soapenv:Header>
soapenv:Body
ns:AcctCustRelSearchRq
ns:RqUID10000000-0000-0000-0000-xxxxxxxxxxxx</ns:RqUID>
ns:MsgRqHdr
ns:ContextRqHdr
ns:NetworkTrnData
ns:TerminalIdentterm id</ns:TerminalIdent>
ns:Nameterm name</ns:Name>
</ns:NetworkTrnData>
ns:ClientApp
ns:OrgFN Org</ns:Org>
ns:Namename</ns:Name>
ns:UserNameuser</ns:UserName>
ns:Version1.0.0</ns:Version>
ns:Channelch</ns:Channel>
</ns:ClientApp>
</ns:ContextRqHdr>
ns:FeeRqHeaders
ns:FeeRqHdr
ns:CostCenterxxxx</ns:CostCenter>
</ns:FeeRqHdr>
</ns:FeeRqHeaders>
</ns:MsgRqHdr>
ns:AcctCustRelSearchSel
ns:AcctKeys
ns:AcctType
ns:AcctTypeValueCCA</ns:AcctTypeValue>
ns:AcctTypeSrcIFX</ns:AcctTypeSrc>
</ns:AcctType>
</ns:AcctKeys>
</ns:AcctCustRelSearchSel>
</ns:AcctCustRelSearchRq>
</soapenv:Body>
</soapenv:Envelope>
:stuck_out_tongue:
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Unfortunately we cannot really help you out with this questions because it goes outside our realm of expertise. We are sure the community might be able to help though.