How to replace script html content in StringBuilder

I have an HTML page in my .Net project as I have one script section

<script language="javascript" type="text/javascript">
    s.property1="|*|property1|*|"
    s.property2="|*|property2|*|"
<script>

      

        
        
        
      

    

In C # code, I read html file and replace "| * | property1 | * |" values ​​given below

StringBuilder siteCode = new StringBuilder();
//code to append html file to StringBuilder(siteCode)

if(xyz!=null)
{
    siteCode.Replace("|*|property1|*|", xyz);
}
else
{
    //remove s.property1="|*|property1|*|"
}

      

        
        
        
      

    

How to remove s.property1 = "|| property1 ||" from StringBuilder(siteCode)

?