It is relatively easy to delete a Personal Best for Workouts and Single exercises in the app.
Here is how to delete the PB for a God workout:
Here is how to delete the PB for a single exercise:
It is also possible to delete runs following the same method, although please be aware that currently it’s not possible to delete runs on iOS.
This also works for PBs that you logged way back at the beginning of being a free athlete. Enter your training history but instead of clicking on “Recents” click on “Workouts”. Now you’ll see a list of all god workouts, click on the one you want to delete and you’ll see a list with all of your times for that one god. Click on the time you want to delete and follow the steps from Ben’s video 
followed your instructions, but when clicking on a particular exercise (over 4 years back) it doesn’t actually open, so I do not get to the screen where I should be able to delete it. I could delete some incorrect scores, but not all. It seems not all exercises are selectable this way. Any advise?
Hi, I had this problem once and I contacted support. They told me that the exercise was done too long ago, and after a long time you cannot delete your PB in the app anymore. They ended up deleting it for me though. @freelectics