Be aware, that changing the initial configuration administrator (XWiki owner, owner of the first page ‘Home’/‘Startseite’ …) may lead to further complications mentioned in xWiki is broken - prop.owner changed and Delete Admin user by mistake.
I am fighting with this issue, because as a user of the wiki, I don’t want to have access to all resources. In the end, the admins should only have access to sensitive data together with one of the managing directors. That also corresponds to the four-eyes principle 
How to set a “page owner” does not solve this issue.
While my initial configurator xwiki-user is deleted, there are a lot of entries in the postgresql-db in the table ‘xwikidoc’ relating to him.
I don’t know too much about xwiki at the moment, we are testing it since yesterday in a docker container - great work you all have done here!
I will come back to this topic again. I hope, I do not offend against the forum guidelines with my first reply. I just try to reconfigure my installation the right way. It would be easier to reinstall - but how does it help on the long run that way?