answer: #Person1# helps Liu Wei to transfer from flight CA621 to flight GB105.
documents: #Person1#: Good afternoon, need any help?
  #Person2#: My name is Liu Wei. I have booked a ticket to Boston three days before.
  #Person1#: That's right and your flight number is CA621.
  #Person2#: But now I want to make a change. Please cancel this flight and transfer me to flight GB105.
  #Person1#: Excuse me, sir. Flight GB105 is one to Milan, are you sure of your change?
  #Person2#: Yes.