help with looping through datagridview rows and update sales rate based on value

[iced8out]

hi guys, so I've been tinkering with this code for about 2 weeks and keep ending up with the same result where the values don't update until a new row is added in the datagridview. so basically what im trying to do is loop through the rows and update the sales rate based on 2 conditions. 1 condition is a value from a column and the 2nd condition is from a text label. here is my code so far any help would be greatly appreciated.

Private Sub DataGridView1_CellValueChanged(sender As Object, e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DataGridView1.CellValueChanged
        Try
            If DataGridView1.Rows.Count > 0 Then
                If txtTaxType.Text = "Inclusive" Then
                    con = New SqlConnection(cs)
                    con.Open()
                    Dim ct As String = "select PRate,PQty,BottleDeposit from product where PID=@d1 and POffer='Yes'"
                    cmd = New SqlCommand(ct)
                    cmd.Parameters.AddWithValue("@d1", Val(DataGridView1.Rows(e.RowIndex).Cells("PID").Value))
                    cmd.Connection = con
                    rdr = cmd.ExecuteReader()
                    If rdr.Read() Then
                        Dim BValue = rdr.GetValue(2)
                        Dim PromoRate = rdr.GetValue(0)
                        Dim PromoQty = Val(rdr.GetValue(1))
                        For Each row As DataGridViewRow In DataGridView1.Rows
                            If Val(DataGridView1.Rows(e.RowIndex).Cells("Qty").Value) >= PromoQty Then
                                DataGridView1.Rows(e.RowIndex).Cells("SalesRate").Value = PromoRate
                            End If
                            If lblpromo.Text >= 0.2 And Val(DataGridView1.Rows(e.RowIndex).Cells("BD").Value) = BValue Then
                                row.Cells("SalesRate").Value = PromoRate
                            End If
                        Next
                    End If
                    con.Close()
        Catch ex As Exception
            MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End Try
    End Sub