Prometheus Alertmanager

I am trying hard to set up the Dashboard, currently working on the Prometheus Alertmanager.

The alertmanager sends out emails correctly now, but the template used is containing wrong links.
Unfortunately, I can not find the template in the place I would expect it to be (from reading the config inside alertmanager)

- /etc/alertmanager/template/*.tmpl

The original template alertmanager/default.tmpl at main · prometheus/alertmanager · GitHub refers to ExternalURL, which should be set from command line when starting the alertmanager Setting web.external-url doesn't work for "Source" link · Issue #2858 · prometheus/alertmanager · GitHub

Further down the email / template, there is a link that should point to prometheus and not the alertmanager. However, the link currently points to the mailserver sending the mail. The link is created from the variable GeneratorURL

I think that both urls should be made available in UCR plus any info on where to find the template(s) would be great.