I am saving textbox text to a DGV and then saving the DGV row to a xml file but i cannot workout how to append instead of overwriting.

Code:
    Public Sub WwriteToDataGridView()
        'save data to DGV
        With Ddata.DataGridView2
            'https://stackoverflow.com/questions/19162248/index-was-out-of-range-must-be-non-negative-And-less-than-the-size-of-the-colle
            ' Write to cell (0,0)
            '.ColumnCount = 6
            .Columns(0).Name = "REGO"
            .Rows(0).Cells(0).Value = OEM_Specs.TxReg.Text
            .Columns(1).Name = "WHEELBASE"
            .Rows(0).Cells(1).Value = OEM_Specs.TxtWheelBase.Text
            .Columns(2).Name = "REAR OVERHANG"
            .Rows(0).Cells(2).Value = OEM_Specs.TxtReOverhang.Text
            'gvm diff
            .Columns(3).Name = "GVM DIFF"
            .Rows(0).Cells(3).Value = TxtTBMeffectGVM.Text
            'tbw
            .Columns(4).Name = "TBM"
            .Rows(0).Cells(4).Value = TxtTowBallMassVan.Text
            'gvm gain/loss
            .Columns(5).Name = "GVM GAIN LOSS"
            Dim GVMVanEffect2 As Double = CDbl(TxtTBMeffectGVM.Text)
            Dim GgvmGainLoss As Double = TBM - GVMVanEffect2
            .Rows(0).Cells(5).Value = GgvmGainLoss.ToString
        End With
    End Sub
Code:
 Public Sub SsaveDataGridViewToDataSet()
        Dim dt As DataTable = New DataTable("data")
        For i As Integer = 0 To Ddata.DataGridView2.ColumnCount - 1
            dt.Columns.Add(Ddata.DataGridView2.Columns(i).Name, GetType(System.String))
        Next
        Dim myrow As DataRow
        Dim icols As Integer = Ddata.DataGridView2.Columns.Count
        For Each drow As DataGridViewRow In Ddata.DataGridView2.Rows
            myrow = dt.NewRow()
            For i As Integer = 0 To icols - 1
                myrow(i) = drow.Cells(i).Value
            Next
            dt.Rows.Add(myrow)
        Next
        dt.WriteXml(My.Computer.FileSystem.SpecialDirectories.MyDocuments & "\weights\data\data.xml")
    End Sub