Mass deletion of pass workouts

So, I bought a used Garmin a few weeks ago, and I've just realised that I've now got an extra 300 or so workouts in my history, mainly in London, which is fortunately not somewhere I've exercised much 😂

Do you have any ideas on how to delete them based on location, or perhaps the source device and them occurring before I got the device?

I've been struggling even to find a place where they're all listed on the website; it was only the profile heat map that made it obvious I'd got a problem!