How do I correct the event date?

I have recently imported two videos into Final Cut Pro. These two videos are old videos from many decades ago but for some reason the creation date is marked as last week (maybe because I transcoded it using another program etc). Therefore naturally, when imported intoe FCPX, the event is grouped into the 2013 year.

I have since when into the videos and changed "Ajust content created date and time" and changed it back to 20 years ago. The video is corrected, but the event is still group in 2013. How do I fix this?