Factory reset & change RAID without losing data

Yep, you clearly added the drive with XRAID enabled, which converted the volume to a redundant RAID1.  There is no way witrhin the confines of the GUI to un-do that.  Your plan will just get you in bigger trouble.

You really should have a backup.  There is an old IT saying "If you only have one copy of something, you must not think it's important."  Some think RAID is a backup (it's not), but you don't even have that.

I have recently posted how to un-do this, but it involves using SSH and the command line.  See the second post in this thread: Reducing-RAID-size-removing-drives-WITHOUT-DATA-LOSS-is-possible.  One false move with this process, and your data is gone.  So if you are not 100% confident in your ability to do it, then it's time to get that much-needed backup and follow the procedure of deleting and re-creating the volume in FlexRAID mode, as you have read elsewhere.

Note that I went on to add the drive back as a group, which expands the existing volume.  But it has a dis-advantage of one drive failure causing loss of all data without even having the speed benefit of RAID0 striping.  You are better off creating a second volume on the second drive, but that does mean you have to manually balace the space used on the two.  You cannot convert the single-drive JBOD to RAID0 (At least, not within the confines of the GUI.  I've not tried it via SSH).