You want the xf_ip table. You just need to find the value associated with that IP and delete all of those records.
I am uncertain if newer MySQL IP functions are appropriate here. But you can run this query to return the most used IP values which is probably good enough to determine which value is the offending IP:
SELECT ip, COUNT(*) AS 'Total', COUNT(DISTINCT user_id) AS 'Unique Users'
GROUP BY ip
ORDER BY Total DESC
Once you have the value you can delete those records with this query: