Rather than writing at length, here is the command to renew an expired MicroK8S certificate.
sudo microk8s refresh-certs --cert ca.crtI have done this many times over the 4 years I have been using Kubernetes with the MicroK8S distribution.
Automatically, once you run the microk8s config view command, the certificate it outputs is already the new one, and it can be used right away in Lens IDE or K9S.