You’ve renewed your Lync 2010 or Lync 2013 certificate through a third party (or even your own) certificate authority, then import the renewed certificate into your server. Now you want to apply it through the wizard, but it’s just not listed. You check the certificate validity through the snap in and realize you don’t have a private key associated with your certificate.
The fix is simple, get the serial number from the certificate, and from an administrative command prompt, run the following:
certutil -repairstore my “Serial Number”
The old certificate as well as the new should be using the same private key, but Windows needs to know that it needs to associate the key with the new certificate. The above command will accomplish that for you.