Check if value already exists before adding values in grid view update quantity VB.NET

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VB

i need add value to DataGridView before add value Check if value already exists if value already exists update value in DataGridView vb.net

What I have tried:

For i = 0 To DataGridView1.Rows.Count.ToString - 1
           If DataGridView1.Rows(i).Cells(0).Value = TextBox1.Text Then
               DataGridView1.Rows(i).Cells(2).Value = DataGridView1.Rows(i).Cells(2).Value + 1
           Else
               Try
                   con = New SqlConnection(cs)
                   con.Open()
                   cmd = New SqlCommand("SELECT ItemID, RTRIM(DishName),'1',Rate from Dish where ItemID like '" & TextBox1.Text & "' order by DishName", con)
                   rdr = cmd.ExecuteReader(CommandBehavior.CloseConnection)
                   While (rdr.Read() = True)
                       DataGridView1.Rows.Add(rdr(0), rdr(1), rdr(2), rdr(3))
                       Dim num1 As Double
                       For j As Integer = 0 To DataGridView1.RowCount - 1
                           num1 = Val(DataGridView1.Rows(j).Cells("Qty").Value) * Val(DataGridView1.Rows(j).Cells("Rate").Value)
                           num1 = Math.Round(num1, 2)
                           DataGridView1.Rows(j).Cells("Amount").Value = num1
                       Next
                       TotalCalc()
                   End While
                   con.Close()
               Catch ex As Exception
                   MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
               End Try
           End If
       Next