Nevermind

but will post what I found if it helps someone else. I found out you can do chat on the mobile app, so I did that during lunch break and SW got his ticket cancelled and rebooked as companion. Points are back in my account.
From reading, you can also cancel and rebook yourself, but run the risk of seats getting snatched out from under you so best to call/chat.
He has a different confirmation number than the rest of us now, so for checkin maybe I should get him the app on his phone so we can do them simultaneously.