@YanezCert To explain in more detail what @JuergenAuer means: certbot and other clients (like used by Plesk) don’t use the same configuration and/or means of file storage and there isn’t any straight forward way to “convert” configurations/files from one client to another. The already created certificates by the ACME client used by Plesk aren’t available to certbot. That’s why it’s most straight forward just to create new certificates.
That said, in theory it’s possible to use the previously issued certificates/private keys et cetera, but that would mean a lot of manual converting without any garuantee it will succeed.
Also, I’m assuming you’re not going to use Plesk any longer? But if you do intent to use Plesk again in the future, please notice the above also goes the other way around: the ACME client used by Plesk can’t use the new certificates issued by certbot automatically.