Sorry for not doing that.
I could create a new blank instance of the excel spreadsheet, but I don't know how to open an existing file, create a duplicate of that file, insert data and save it in a new name.
The code that I used to write data to a blank file is :-
protected void btnSubmission_Click(object sender, EventArgs e)
{
Microsoft.Office.Interop.Excel.Application xlapp = new Microsoft.Office.Interop.Excel.Application();
Workbook wb = xlapp.Workbooks.Add(XlSheetType.xlWorksheet);
Worksheet ws = (Worksheet)xlapp.ActiveSheet;
xlapp.Visible = true;
String s1 = TextBox2.Text;
ws.Cells[4,4]=s1;
}