Though your original post stated clearly that you were arriving by train, it didn't indicate where you were arriving. It is now clear that you are arriving by train at CDG and taking a flight from that airport. I know neither the terms of your ticket as far as changes are concerned, nor from whom you purchased the ticket. In addition, I don't know if you will be checking luggage on your flight to Hanoi. Unfortunately, under the circumstances, I'm not able to offer further advice. It does still seem to me, however, that your original plans do not allow sufficient time to transfer from the train to the plane at CDG, even if the connection you have scheduled is legally acceptable.