Delete a warning

[Smethead]

i'm not sure if there is buildin function in that mod for that, or if it does that automaticly, but in case it was just a special case for this time only, try by editing that user's warn in the phpmyadmin > mybb_users > reportwarnings column
find that user's record and edit that part

however you know that you can increase the max warns through the Admin CP > Board Settings > Change > Alternative Rep System

regards

That's totally correct.
However, if you delete the reportwarning using phpmyadmin, the warning message will not be removed from the user's inbox.