My apologies. The link I provided only clears the rating cache, rather than the logs.
Unfortunately, K9 was designed to keep at least the last 3 days of Admin Logs stored for security purposes. After 3 days, the logs are deleted. I will submit your thoughts to our product development team to see if there is any way to include a feature to clear Admin Logs in a future version of K9.
I apologize for the trouble.