Move down Cells because the Data has been Over write in Excel - vb.net

Question

Good Afternoon
I have an Excel File this is what it looks.
and I have a VB.Net Program that looks like this.
Now after clicking the Print Transmittal Form the data from Datagridview will transfer into the Excel Format that I created but theres something wrong and here is the output.
The data overwrite this part.
How can I prevent that? Instead of over writing the cells the overwritten part will move down based on how many data on datagridview.
Here is my code.
If DataGridView1.Rows.Count = 0 Then
MsgBox("Nothing to Export")
Else
Dim ExcelApp As Object, ExcelBook As Object
Dim ExcelSheet As Object
Dim rowIndex As Integer = 1
Dim total As Double = 0
ExcelApp = CreateObject("Excel.Application")
ExcelBook = ExcelApp.Workbooks.Open("c:\SR Transmittal.xlsx")
ExcelSheet = ExcelBook.WorkSheets("Transmittal Form")
rowIndex += 11
With ExcelSheet
For i As Integer = 0 To DataGridView1.Rows.Count - 1
Dim columnIndex As Integer = 0
Do Until columnIndex
ExcelSheet.Cells(i + 12, columnIndex + 2).Value = DataGridView1.Item("ItemCode", i).Value.ToString
ExcelSheet.Cells(i + 12, columnIndex + 3).Value = DataGridView1.Item("Description", i).Value.ToString
ExcelSheet.Cells(i + 12, columnIndex + 4).Value = DataGridView1.Item("RequestedQty", i).Value.ToString
ExcelSheet.Cells(i + 12, columnIndex + 5).Value = DataGridView1.Item("UOM", i).Value.ToString
ExcelSheet.Cells(i + 12, columnIndex + 6).Value = DataGridView1.Item("UnitPrice", i).Value.ToString
ExcelSheet.Cells(i + 12, columnIndex + 7).Value = DataGridView1.Item("Total", i).Value.ToString
ExcelSheet.Cells(i + 12, columnIndex + 8).Value = DataGridView1.Item("Remarks", i).Value.ToString
.cells(i + 12, columnIndex + 4).NumberFormat = "#,##0.00"
.cells(i + 12, columnIndex + 6).NumberFormat = "#,##0.00"
.cells(i + 12, columnIndex + 7).NumberFormat = "#,##0.00"
columnIndex += rowIndex
.Columns("A:Z").EntireColumn.AutoFit()
.Columns("A:Z").EntireColumn.Font.Size = 9
Loop
Next
End With
ExcelApp.Visible = True
ExcelSheet = Nothing
ExcelBook = Nothing
ExcelApp = Nothing
End If
TYSM for help

Answer 1

Recently worked on something similar, I achieved it by inserting a new row prior to poplulating with data. For you it would look something like:
For i As Integer = 0 To DataGridView1.Rows.Count - 1
oSheet.Range(oSheet.Cells(i + 12, 2), oSheet.Cells(i + 12, 8)).Insert(Shift:=Excel.XlDirection.xlDown)
'... add row data
Also, FWIW, is the use of columnIndex and its Do Until entirely redundant? The loop will only ever run once (prior to having 12 (rowIndex) added to it?