Set Parent field from Child document

Sub Click(Source As Button)
        Dim workspace As New NotesUIWorkspace
        Dim session As New NotesSession
        Dim uidoc As NotesUIDocument
        Dim db As NotesDatabase
        Dim response As NotesDocument
        Dim parent As NotesDocument
        Dim item As NotesItem
        Dim ParentDocumentUNID As String
        Dim strCompleted As String
      
        Set db = session.CurrentDatabase
        Set uidoc = workspace.CurrentDocument
      
        uidoc.EditMode = True
        Call uidoc.Save
      
        strCompleted = uidoc.FieldGetText("Completed")
      
        Set response = uidoc.Document
        ParentDocumentUNID = response.ParentDocumentUNID
        Set parent =  db.GetDocumentByUNID( ParentDocumentUNID )
        parent.EditMode = True
      
        Set item = parent.ReplaceItemValue( "ResponseCompleted", strCompleted )
      
        Call parent.Save( True, False )
        Call uidoc.Close
        Delete uidoc
      
End Sub