Given that presumably you are looking for compensation based on delayed arrival, the best thing to do first is to use the free "flight check" offered by any of the various claims agencies.

If they think you're onto a winner, then you know you have a case worth pursuing. (And you can try and pursue it yourself, it is just useful to use these agencies' checkers to make sure that you are actually on to a winnable case)

https://www.euclaim.co.uk