Orphaned apps in gitlab-managed-apps namespace


I upgraded our gitlab server to 11.6 and decided to use the new group Kubernetes feature.
The group k8s only allows you to install helm, nginx and cert-manager from gitlab.
But our runner was previously installed using gitlab in gitlab-managed-apps.

I used to be able to use the command helm list --tiller-namespace gitlab-managed-apps from my laptop and manage those apps if needed.
But now I get a Error: transport is closing which probably means that tiller in that namespace is now configured to use TLS. And Gitlab must be managing that now.

So how in the world am I supposed to cleanup the GitLab abandoned apps in that namespace so I can manage them myself?
I’ve already created my own gitlab runner deployment in the cluster using helm, but there is no way to delete the one in the gitlab-managed-apps namespace.