You can also phone the airline and give information that way as well if you did not want to wait until you get your tickets.
All you need to give them is name of persons traveling flight number and time and from which airport you are flying from and of course passport information etc..
You would have the flight information as this would be on the itinarary that the travel agent sent you confirming your booking if booked via a travel agent.
Quite a few of our guests who have booked their flights via a travel agent have given their API this way by calling the airline.