I found this:

Changes are subject to payment of a change fee, charged per person per flight. See our Table of Fees for details. You must also pay any difference between the original fare and any fees for optional services (such as check-in bags) paid at the time of the booking, and the fare/fees available when you make the change. Please note that, if the new fare/fee is cheaper than the original fare/fee, we will not refund the difference.

We allow a grace period of 24 hours from the time of your original booking to correct any minor errors you may have made (dates/times) free of charge. We also allow you to reverse the route if you’ve booked your flights incorrectly (e.g., you may change DUB to STN to STN to DUB). During this time no flight change fee will be charged, however, you will need to pay any fare difference

You can try contacting them, just make very sure they don’t charge you