score:1
In this case I contacted Expedia first. The staff on the phone said he believes it would not be a problem, but if I feel uneasy, he would report the number to Vietnam Airlines.
Actually, it seemed to me that the staff also didn't know much about what to do. So I just informed him of my new passport number and hung up the phone.
I also asked my friend who is a flight attendant of Vietnam Airlines, and she said I can just contact Vietnam Airlines and change it for free.
I'm still not sure which I should contact first in these cases, but it may be true that both are fine.
Upvote:3
As it's not unusual for a new passport to be issued between the time a ticket is purchased and the actual flight, it shouldn't be a problem. Carry both the old and new passports with you, just in case you're questioned about it when you check in at the airport. Your passport number is not on your ticket, it's in your passenger record and having both passports should be sufficient. You should just have to update your Expedia account.