If you have either got the Delta booking reference (unlikely as booked via
travel agent/ Air France) or your eticket number (13 digits starting with 006) then you should be able to change your seats on delta.com
Click on the Traveling and Check In tab and then on Itineraries & Check-in and it will give you the option to retrieve your itinerary using either SkyMiles Number, Confirmation Number (Delta booking reference), Credit Card Number
or eTicket Number. You will also need to enter one name on the booking. This should then bring you itinerary up. Underneath this is another box that says Your Seating. You can then use the Select/Change link which should allow you to do the seating.
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