Solutions
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polishprocessors's post in Array drive in Unassigned Drives was marked as the answerOk, I found this, which I believe is the correct procedure:
https://docs.unraid.net/unraid-os/manual/storage-management/#rebuilding-a-drive-onto-itself
It just looks like that 10TB drive is DOA and, because of my mess-up, I'll need to rebuild the 14TB drive then look into replacing the 10TB as well