HELP - MySQL at full load!

[Lolli]

Hi, I have a problem!

I installed this plugin: Restore Posts and Threads of Deleted User.

https://vborg.vbsupport.ru/showthread.php?t=242229

I made a mistake and instead of entering the id of the destination user, I entered his nickname ...

Now I have MySQL burdened by this query:

UPDATE post
SET userid = 'nickname2'
WHERE username = 'nickname1';

There is no way to end it. I restarted Apache and MySQL, I rebooted the server, I have kill (KILL, KILL QUERY) the query to MySQL after reading processes with SHOW PROCESSLIST, but the query always returns.

I noticed that MySQL returns free when Apache is stopped. This could mean that the query returns because it is buffered in Apache or PHP. How can I do to clear this buffer?

How to solve this bizarre case?