which I found via rotatedlife's post in
https://www.reddit.com/r/MacOS/comments/74scld/unable_to_turn_on_filevault_on_high_sierra_apfs/
http://www.theinstructional.com/guides/how-to-re-run-the-os-x-setup-assistant
https://www.engadget.com/2014/08/23/how-to-make-os-x-mavericks-re-run-the-setup-assistant/