The agent at the call centre couldn’t answer your question?

If he/she didn’t know - and since you’ve exhausted every “non airport” option - that would probably indicate that there’s no way of doing it in advance ... and you’ll need to see an agent at check-in at the airport to correct it.

I’m not sure why, but it seems that all airlines (that I’ve used, at least) lock both passport info and KTN numbers once they’re entered on a reservation — they can’t be edited afterwards.