Gitlab Autodevops: Resetting a kubernetes cluster - gitlab

Question

I'm currently on a self-hosted Gitlab 11.9 instance. I have the ability to add a kube cluster to projects on an individual level, but not on a group level (that was introduced in 11.10).
I created a Kubernetes cluster on AWS EKS and successfully connected it to Gitlab's Autodevops for a specific project. I was able to successfully install Helm tiller, Prometheus, and Gitlab Runner. Autodevops was working fine for that project.
Before I discovered that having a cluster run at the group-level was introduced in Gitlab 11.10, I disconnected the kube cluster from the first project and connected it at the group-level. I successfully installed Helm Tiller but failed to install Ingres or Cert-Manager. After I discovered my version doesn't contain group-level autodevops functionality, I connected the cluster to another, different, application and attempted to install Prometheus and Gitlab Runner. However, the operation failed.
My pods are as follows:
% kubectl get pods --namespace=gitlab-managed-apps
NAME READY STATUS RESTARTS AGE
install-prometheus 0/1 Error 0 18h
install-runner 0/1 Error 0 18h
prometheus-kube-state-metrics-8668948654-8p4d5 1/1 Running 0 18h
prometheus-prometheus-server-746bb67956-789ln 2/2 Running 0 18h
runner-gitlab-runner-548ddfd4f4-k5r8s 1/1 Running 0 18h
tiller-deploy-6586b57bcb-p8kdm 1/1 Running 0 18h
Here's some output from my log file:
% kubectl logs install-prometheus --namespace=gitlab-managed-apps --container=helm
+ helm init --upgrade
Creating /root/.helm
Creating /root/.helm/repository
Creating /root/.helm/repository/cache
Creating /root/.helm/repository/local
Creating /root/.helm/plugins
Creating /root/.helm/starters
Creating /root/.helm/cache/archive
Creating /root/.helm/repository/repositories.yaml
Adding stable repo with URL: https://kubernetes-charts.storage.googleapis.com
Adding local repo with URL: http://127.0.0.1:8879/charts
$HELM_HOME has been configured at /root/.helm.
Tiller (the Helm server-side component) has been upgraded to the current version.
Happy Helming!
+ seq 1 30
+ helm version
Client: &version.Version{SemVer:"v2.12.3", GitCommit:"eecf22f77df5f65c823aacd2dbd30ae6c65f186e", GitTreeState:"clean"}
Error: cannot connect to Tiller
+ sleep 1s
Retrying (1)...
+ echo 'Retrying (1)...'
+ helm version
Client: &version.Version{SemVer:"v2.12.3", GitCommit:"eecf22f77df5f65c823aacd2dbd30ae6c65f186e", GitTreeState:"clean"}
Error: cannot connect to Tiller
...
+ sleep 1s
+ echo 'Retrying (30)...'
+ helm upgrade prometheus stable/prometheus --install --reset-values --tls --tls-ca-cert /data/helm/prometheus/config/ca.pem --tls-cert /data/helm/prometheus/config/cert.pem --tls-key /data/helm/prometheus/config/key.pem --version 6.7.3 --set 'rbac.create=false,rbac.enabled=false' --namespace gitlab-managed-apps -f /data/helm/prometheus/config/values.yaml
Retrying (30)...
Error: UPGRADE FAILED: remote error: tls: bad certificate
This cluster doesn't contain anything else except for services, pods, deployments specifically for autodevops. How should I go about 'resetting' the cluster or uninstalling services?