Good luck with that one! I booked mine through Hotwire. Tried Aer Lingus...used the 516 area code number for reservations that I found on the web site. Waited almost 45 minutes for them to pick up. Then called Hotwire...explained to them I needed seats...they called and it took about 20 minutes that time. Hotwire then put me through and I spoke directly with Aer Lingus to get my seats.
When questioned about it, the response from Aer Lingus was that third parties actually control the tickets...not Aer Lingus. Haven't heard that one before. All changed had to come from the place you booked your ticket. But they just put me back on the phone with Aer Lingus to get it done anyways! Go figure.
Had to repeat the same process to pre-book meals and get the exit row seat for our overseas flights. One nice thing is that normally Aer Lingus won't let you book inter-Europe seats in advance for free...wanted a nominal fee for that. When Hotwire connected me, they booked them for free.
Good luck.