EX4100 - How can I downgrade from RAID1 to JBOD (without formatting all my drives)

I have EX4100 with 2 wd 4tb HDD with RAID1. I want to move to JBOD but when I try switching to JBOD I get a warning that both drives will be formatted. I need 1 drive to be kept intact. How can I downgrade rather than switching to JBOD?