Listbox Content Control - Reset default?

[KilpAr]

Let's say we have a list box. We have there a prompt "Pick value" and the options are "1", "2" and "3". User picks value "3". Now in order to reset this value to "Pick value", what do I need?

This

    Dim obj
    Set obj = ActiveDocument.ContentControls(2)
    obj.Range.Text = obj.PlaceholderText.Value

fails to "You are not allowed to edit this selection because it is protected".