Thank you for the prompt and informative reply.
Mark Sapiro wrote:
... If you are an owner or moderator of a list or a superuser, you can handle moderation requests via Postorius. If you are a list owner or a superuser, you can manage owners and moderators via Postorius.
Yes, I would like to do that.
You can add superusers via the command line django admin createsuperuser command.
For the reference of others like me, createsuperuser will allow you to create a user with a non-unique email address. I strongly recommend against that.
mailman shell gave me:
from django.contrib.auth.models import User User.objects.filter(is_superuser=True) <QuerySet [<User: admin>, <User: xxxx>]>
I dredged a password for admin out of my memory and was able to perform the moderation request. I also set a new list owner.