To uninstall KubeDB Community edition, run the following command:
In Helm 3, release names are scoped to a namespace. So, provide the namespace you used to install the operator when installing.
$ helm uninstall kubedb-community --namespace kubedb
If you prefer to not use Helm, you can generate YAMLs from KubeDB chart and uninstall using
$ helm template kubedb-community appscode/kubedb-community --namespace kubedb | kubectl delete -f -