old ssl certificate is still being given out by IIS

netsh http show sslcert
This showed me two SSL Certificate bindings. One on IP:Port with the correct certificate and one on IP:Port :::443 with an expired certificate. I opened CertMgr.msc for the Local Computer (see here for instructions) and searched for the invalid certificate and discovered it had expired.

To resolve the issue I did the following

netsh http delete sslcert ipport=:::443
iisreset /restart