Can I add a new drive (seperate volume) without starting over?

Hi there, I am currently running two 4tb drives in Raid 0, and have just added a 3rd drive (WD Red 8tb) and wanted to use it as a separate 2nd volume. Dashboard says the drive is ok, but I have no option to create a volume - and the main unit is showing a red led for that bay. Is what I’m trying to do even possible or do I need to effectively wip the other two drives and start all over?

Many thanks in advance for any help!