can someone help me take a look my code

Private Sub txtsg2_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtsg2.TextChanged
        Dim TB1Integer As Double
        Dim TB2Integer As Double
        If Double.TryParse(txtsg1.Text, TB1Integer) AndAlso Double.TryParse(txtsg2.Text, TB2Integer) Then
            Total1_2.Text = CStr(TB1Integer + TB2Integer)
        Else
            MessageBox.Show("Please enter a number in both boxes.")
        End If
    End Sub

i try writing this code 

  Dim mystring As String
        mystring = TextBox5.Text

        Dim arr() As String = {mystring}
        Dim value1 As String
        value1 = TextBox5.Text
      
        If value1 = Array.Find(arr, Function(x) (x.StartsWith("."))) Then
            MessageBox.Show("Pls Make Sure You Fill In Correct Number")
        Else
            MessageBox.Show("SAVE DATA SUCCESS")
        End Ifbut i fail to find (.)decimal point

can someone help me take a look and give me an advise or comment 

thanks a lot