Refer below article.

[Solution] ASP.Net GridView Export to Excel: The file you are trying to open is in a different format than specified by the file extension

Dim xlapp As Object
xlapp = CreateObject("Excel.Application")

Dim xlWorkBook As Excel.Workbook
Dim xlWorkSheet As Excel.Worksheet

Dim FilePath As String = "C:\1.xls"


If System.IO.File.Exists(FilePath) Then
	xlWorkBook = xlapp.workbooks.open(FilePath, False)
Else
	xlWorkBook = xlapp.workbooks.add()
End If


If String.IsNullOrEmpty(xlWorkBook.Path) Then
	xlWorkBook.SaveAs(FilePath, Excel.XlFileFormat.xlWorkbookNormal)
End If

If xlWorkBook.Sheets.Count() < 1 Then
	xlWorkSheet = CType(xlWorkBook.Worksheets.Add(), Excel.Worksheet)
	xlWorkSheet.Name = "Log Sheet"
Else
	xlWorkSheet = xlWorkBook.Worksheets(1)
End If

Dim SheetRow As Integer = 0

	For SheetRow = 1 To xlWorkSheet.Rows.Count
		If Trim(xlWorkSheet.Cells(SheetRow, 1).value) = "" Then
					xlWorkSheet.Name = "Log Sheet"

                        xlApp.Cells(1, 1) = "File access path "
                        xlApp.Cells(1, 2) = "File Name"
                        xlApp.Cells(1, 3) = "File Access By User"
                        xlApp.Cells(1, 4) = "Date"
                        xlApp.Cells(1, 5) = "Time"

                        xlWorkSheet.Columns.Range("A1:E1").Font.Bold = True
                        xlWorkSheet.Columns.Range("A1:E1").Font.Color = Color.Blue
                        xlWorkSheet.Columns.Range("A1:E1").Font.Size = 15

                        Exit For
                    End If
Next

  Dim iRow As Integer = 0
                Dim iCol As Integer = 0

                For iRow = 3 To xlWorkSheet.Rows.Count
                    If Trim(xlWorkSheet.Cells(iRow, 1).value) = "" Then

                        xlWorkSheet.Cells(iRow, 1).Value = sDirectory
                        xlWorkSheet.Cells(iRow, 2).Value = sFileName

                        Dim AccessDate As String = String.Empty
                        Dim AccessTime As String = String.Empty

                        AccessDate = AccessDate.Trim & DateTime.Now.Day
                        AccessDate = AccessDate.Trim & "-" & DateTime.Now.ToString("MMMM")
                        AccessDate = AccessDate.Trim & "-" & DateTime.Now.Year & " "

                        AccessTime = AccessTime.Trim & DateTime.Now.Hour
                        AccessTime = AccessTime.Trim & ":" & DateTime.Now.Minute & " "
                        AccessTime = AccessTime.Trim & " " & DateTime.Now.ToString("tt")


                        xlWorkSheet.Cells(iRow, 3).Value = My.Settings.timeSheetLoginUserType
                        xlWorkSheet.Cells(iRow, 4).Value = AccessDate
                        xlWorkSheet.Cells(iRow, 5).Value = AccessTime



                        Exit For        ' BAIL OUT IF REACHED THE LAST ROW.
                    Else
                        
                    End If

                Next

xlWorkBook.Save()
xlApp.DisplayAlerts = False

xlWorkBook.Close()

System.Runtime.InteropServices.Marshal.ReleaseComObject(xlApp)
xlWorkSheet = Nothing

System.Runtime.InteropServices.Marshal.ReleaseComObject(xlWorkBook)
xlWorkBook = Nothing

System.Runtime.InteropServices.Marshal.ReleaseComObject(xlApp)
xlApp = Nothing