I wish to revise my above answer, but I can't edit it for some reason so here's the newer version:
The good news is you don't need a helpdesk ticket.
If the unwanted KOM was due to the GPS recording device still functioning after the bike ride (on your car drive home), the best way to handle the situation is to use the cropping tool. With it you can remove the offending, latter portion of the ride and save the legitimate (earlier) portion of your activity. You will then lose the KOM. You can also crop from the beginning of the activity, if that's where the unwanted KOM is. Years ago I saw a few occasions where the device records poorly in the first few minutes of the ride because the satellite lock is poor. This happens less frequently now with the newer bike computers.
Since the cropping tool only works for the beginning and ending portions of a ride, for unloved KOM segments elsewhere in the activity, several options exist: You can flag the activity... yes, you can flag your own activity. That will remove that ride from the leaderboards. You'll be asked for a reason for the flag, just choose "bad GPS data" as the reason. One drawback is the activity page will reflect the flag, but if you do this a few days after your ride, probably nobody will notice the flag, and if they do... so what?
You could edit the activity and mark it as viewable only to followers. This removes the activity from leaderboards. A less desireable option might be to edit your ride and mark it as a "private activity". This will remove it from the leaderboards, but then the activity will be hidden from anyone else, even your followers or people viewing your profile page.
Another option is to change the activity type to "workout". This will eliminate all segments from that ride, but the activity page will still show the map, distance and average speed. One drawback here is that the mileage you rode will not be reflected in the yearly and lifetime stats on your profile page.
An obscure, more cumbersome option exists for a segment somewhere in the middle of the ride. The little used split tool permits you to split the activity into two or three seperate activities. If you're good at it, you can "split out" an unwanted portion and wind up with two, legitimate activities. I just wanted to mention that for the sake of clarity, I think that it will be difficult for most to accomplish the task this way.
Sources:
https://support.strava.com/hc/en-us/articles/216919437-Crop-Tool-for-Activities
https://support.strava.com/hc/en-us/articles/221033867-Activity-Split-Tool
https://support.strava.com/hc/en-us/articles/216919377-Activity-Privacy-Controls
