Purge data from uninstalled app Univention-Dashboard
Uninstall the app through the appcenter or use command line to uninstall. Make sure the app including the Dashboard client is uninstalled on every server.
Purge the data directories by removing the directories:
rm -rf /var/lib/univention-appcenter/apps/prometheus/ rm -rf /var/lib/univention-appcenter/apps/admin-dashboard/
Now the app and all data is purged and you can re-install the app if needed.