Thanks! So I booked a TYO - USA 12/12 and then a USA-TYO 12/26. The one I want to keep is the USA- TYO 12/26 but the agent is saying he can't cancel just part of the RT. Is there a magic word or something to it to work? Or am I doing this incorrectly?

Edit: Did try to cancel the segment right after looking so not sure if there was a time limit before changes can be made?
Edit 2: After maybe 15-30 mins, I was able to manage the trip online and attempt to cancel the unwanted segment. However, I keep getting an error. Spoke to a rep and they said that it's due to no availability on 12/26 since canceling one segment would make it into a new reservation. I just think she was making things up and the constraints come from the fact that their calendar is blocked out for the last week of the year. Going to wait a few days for the calendar to open up and make the change then. Any thoughts?