how to stop show message or exit for in the example ?

how to stop show message or exit for When the condition is checks , Iam try (exit for) but dont stop (for , next)

please help

Private Sub Table_1DataGridView_CellStateChanged(sender As Object, e As DataGridViewCellStateChangedEventArgs) Handles Table_1DataGridView.CellStateChanged
        For i As Integer = 0 To Me.Table_1DataGridView.RowCount - 2
            For j As Integer = i + 1 To Me.Table_1DataGridView.RowCount - 2
                If Table_1DataGridView.Rows(i).Cells(1).Value = Table_1DataGridView.Rows(j).Cells(1).Value Then
                    MessageBox.Show("duplicate value : " & Table_1DataGridView.Rows(i).Cells(1).Value)
                    Table_1DataGridView.Rows(i).Cells(1).Selected = True
                    Exit For
                End If
            Next
        Next
    End Sub