I’m confused by this just because I thought earlier you said that you already have a copy of privkey.pem, unless I misunderstood you. You were saying that you already had a copy of the private key.
@JuergenAuer’s point before is that if you don’t have the private key, you can’t regenerate it—it’s secret information that only exists on your server, and can’t practically be derived from public information. That’s what makes the certificate meaningful, because it refers to a key that only you possess, and therefore your possession of that key can be used by others to confirm your identity.