Write data from datatable to existing csv file in new worksheet

Question

I am trying to write data from datatable to cs file in c#. the problem is that i want to write datatable in new worksheet in existing csv file

I have already the function to write data from datatable to new csv file. any help please?

public void CreateCSVFile(DataTable dt, string strFilePath)  
{  
    try  
    {  
         StreamWriter sw = new StreamWriter(strFilePath, false);  
         int columnCount = dt.Columns.Count;  
         for (int i = 0; i < columnCount ; i++)  
         {  
            sw.Write(dt.Columns[i]);  
            if (i < columnCount - 1)  
            {  
              sw.Write(",");  
            }  
         }  
         sw.Write(sw.NewLine);  
         foreach (DataRow dr in dt.Rows)  
         {  
            for (int i = 0; i < columnCount ; i++)  
            {  
              if (!Convert.IsDBNull(dr[i]))  
              {  
                sw.Write(dr[i].ToString());  
              }  
              if (i < columnCount - 1)  
              {  
                sw.Write(",");  
              }  
            }  
            sw.Write(sw.NewLine);  
         }  
         sw.Close();  
    }  
    catch (Exception ex)  
    {  
         throw ex;  
    }  
}