Depends where the Checkmk server is located.
Nitin, can you please confirm that you set-up Checkmk inside a Kubernetes cluster and you are trying to monitor that cluster? Because every other step depends on that.
If Checkmk is inside the Kubernetes cluster, than Checkmk has to contact the Kubernetes API server via the internal Kubernetes network and you have to ensure that this internal K8s service is accessible for Checkmk.
If Checkmk is outside the Kubernetes cluster, follow the steps in the documentation as pointed out by Sudhir.
I can only recommend to run Checkmk in a Kubernetes cluster, if you are an absolute Kubernetes expert and have deep expertise of Kubernetes networking. If you are not too familiar with Kubernetes, please run Checkmk on a dedicated VM.