I didn't understand a single word, but it seem you need something as following
var excelApp = new ApplicationClass {Visible = false};
var excelWorkbooks = excelApp.Workbooks.Open("yourfilepath");
var excelWorkSheet = (Worksheet) excelWorkbooks.Sheets[yourWorkSheetNumber];
excelWorkSheet.Cells[row, column] = yourvalue;
excelWorkbooks.Save();
excelApp.Quit();
Marshal.ReleaseComObject(excelWorkSheet);
Marshal.ReleaseComObject(excelWorkbooks);
GC.Collect();
GC.WaitForPendingFinalizers();