score:2
If you have added your friends to your own United profile as "saved travelers" you can see and edit them there under "Profile & Preferences"->"Personal Information"->"Saved Travellers". That's good practice anyway, since it can help in cases where they travel and you are not around (for any reason).
If you didn't save them you probably have to call United. I would add them to your profile and then ask the United agent to connect them to the booking.