Delete activity from Training Status, Load and other FirstBeat metrics

Long story short I started my run and forgot to connect external HR strap. I didn't realize it only after the run that HR was collected from oHR. oHR doesn't work for me during an activity at all and I don't use it for this reason (see graphs below). This HR is my Zone 5 and it's ridiculous "smart" watch thought one is able to hold Zone 5 for 90 minutes without complaining. On the other hand oHR proved to be very good cadence sensor. :-) Anyway, mistakes were made.

Is there any way how to remove that incorrectly recorded activity from Training status, Load, etc.? I tried deleting from the watch, deleting in Garmin Connect, re-sync to no avail. I think of only other way to factory reset the watch. It might be better than dealing with incorrect stats for next 4 weeks or so.