How to put a field coming from <xsl: value-of select = "#" /> inside a tag? - xslt

Question

I can not add within a tag a field with the (<xsl:value-of select=)
I'm creating an XSLT template that transforms data from an Excel into XML. Everything is working fine but now I wanted to add to the userdata tag the username of excel (#User_Name).
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl">
<xsl:template match="/">
<tXML>
<Header>
<Source>TESTE</Source>
<Action_Type>Upgrade</Action_Type>
<Message_Type>User</Message_Type>
<Company_ID>200000002</Company_ID>
<Msg_Locale>English (United Kingdom)</Msg_Locale>
<Internal_Date_Time_Stamp>08/09/2017 17:35:00</Internal_Date_Time_Stamp>
</Header>
<Message>
<xsl:for-each select="//rs:data">
<xsl:apply-templates/>
</xsl:for-each>
</Message>
</tXML>
</xsl:template>
<xsl:template match="//z:row">
<UserData User_Name="{#User_Name}">
<xsl:value-of select="#User_Name"/>
<User>
<Company_Name>
<xsl:value-of select="#Company_Name"/>
</Company_Name>
<Location_Name>
<xsl:value-of select="#Location_Name"/>
</Location_Name>
<Role_Name>
<xsl:value-of select="#Role_Name"/>
</Role_Name>
<User_Name>
<xsl:value-of select="#User_Name"/>
</User_Name>
<First_Name>
<xsl:value-of select="#First_Name"/>
</First_Name>
<Last_Name>
<xsl:value-of select="#Last_Name"/>
</Last_Name>
<Solutions>
<RestrictedSolution>TESTE</RestrictedSolution>
</Solutions>
</User>
</UserData>
</xsl:template>
</xsl:stylesheet>