To install domain-exporter you need.
helm repo add zifter https://zifter.github.io/helm-charts/Be aware, prometheus CRD must be installed before installing this chart.
Install chart with necessary domains list to specific namespace, where prometheus-operator will be able to discover rules, service monitor and etc:
helm install domain-exporter zifter/domain-exporter --namespace monitoring --set "domains={google.com,reddit.com,amazon.com}"