1. Go to "Settings -> Configure KvIRC"
  2. Go to "Connection -> advanced"
  3. On the tab "SSL" check "Use ssl certificate" and "Use SSL private key" and point both to the mynick.pem file you created.
  4. Change your connection settings and enable the SSL option. Remember to make sure your using port 6697 or 9999.

Once done, read how to add your certificate's fingerprint to N.