Autodetect Prometheus install

I am using the Cluster Applications project to install my cluster applications.

I have installed Prometheus on my Kubernetes cluster. Now I would like to integrate this Prometheus installation into my Gitlab environment. But Gitlab cannot automatically recognize my Prometheus installation.

When I look at the documentation it should work:
https://docs.gitlab.com/ee/user/project/integrations/prometheus.html#managed-prometheus-on-kubernetes

This script also works fine:

POD_INFORMATION = $ (kubectl get pods -n gitlab-managed-apps | grep 'prometheus-prometheus-server')
POD_NAME = $ (echo $ POD_INFORMATION | awk '{print $ 1;}')
kubectl port-forward $ POD_NAME 9090: 9090 -n gitlab-managed-apps

How does Gitlab autodetect the Prometheus installation on my Kubernetes cluster?