Hi all

Due to a recent personal situation, I had to fly GCM > EDI (via GCM>ATL on DL, and then ATL>AMS and AMS>EDI on KLM) and have a return leg (EDI>CDG, CDG>ATL both on AF then ATL>GCM the following day on DL) booked for just over a week from now. Unfortunately, due to unforeseen circumstances, I am going to have to stay in the UK longer than expected and so I need to move the return leg back a week or so. I tried doing this online but when I try I just get an error message if I select any day other than the originally-scheduled day. It does offer me one alternative flight on the same day as originally scheduled but of course that is of no use to me. I don't want to cancel and book a one-way as that is ruinously expensive.

Is this just an error I can expect to be resolved or do I need to call or use chat online? Is what I am trying to do even allowed?

In terms of possibly relevant info, I am booked in business (except for ATL>GCM which is Comfort+), am a Flying Blue member but don't have any Skyteam elite status. The booking is all on one ticket which was bought through Delta's website (all the flights appear in the Delta app and was able to get the boarding passes for the outbound journey on the Delta app).

Grateful for advice in advance.