How to fully reset Let's Encrypt ACME plugin for a specific certificate?

[Stilez]

I've been testing the Let's Encrypt ACME plugin in the staging envioronment.

I want to force the plugin to revalidate the DNS ownership, but can't figure how to do it.
I've deleted the private key and revoked the existing certificate in the GUI, I've deleted all the files I dare from /var/etc/acme-client in Console, but whatever I have tried, when I click the GUI button to forcefully (re-)issue the selected certificate, the log contains this:
"<MYDOMAIN.COM> is already verified, skip dns-01"
How do I reset the client so I don't get this, and so it's forced to reverify DNS-01?