You can add this code to the button in FORM2 which open FORM3.
Dim frm3 As New FORM3()
If frm3.ShowDialog(Me) = Windows.Forms.DialogResult.OK Then
Me.DoWhatYouWantWithThisValue(frm3.SelectTextBox.Text)
End If
When the user select a company from the list in FORM3 you must set:
Me.DialogResult = Windows.Forms.DialogResult.OK