Hey @wylie ! Thanks for your feedback
I followed your link which indicates to see the page https://www.elastic.co/guide/en/kibana/7.6/settings.html for settings but no mention of the setting "server.uuid"
Finally I found a topic with the solution : stop kibana on one of the two Kibana server, remove /var/lib/kibana/uuid and restart. This will create a new uuid.
So I think documentation can be updated to integrate this setting 