If you left rep which you want to delete (for any reason), you can do it within 5 minutes of leaving the rep by doing the following:
1) Go to: https://pokerfraudalert.com/forum/usercp.php
2) Scroll down to the "Latest Reputation Given" box
3) When you see the rep comment you left (should be at or near the top of that box), there will be a prominent "Delete" button next to it. Press that button, and the rep comment is gone!
Again, if you take longer than 5 minutes, this won't work. This is intentional, because the feature is there in order for you to correct erroneous rep, not to take back rep you left awhile ago.
Note that this feature existed years ago, through a mod I did. However, it broke in early 2019 when I changed vBulletin versions, and it was only fully fixed tonight.