Originally Posted by
corporate-wage-slave
You should invite your contact to find an agent wearing a blue name badge since they have full ticketing skills. However other agents can also do it too, so long as there is an hour to go before the new flight. It cab be done in zone E or A landside, or at Customer Service desks in Flight Connections. It's marginally easier if they haven't checked in for the original flight. If not, it can still be done at Customer Services in Galleries South.
Just to report back on this: the transfer had to be landside, as expected. He went to the desk as instructed, tap tap tap for a few seconds and it was done. About as easy as it is possible to imagine! Very grateful for the help on this - telling a teenager how to go about this sort of stuff does not always lead to such straightforward results.