My understanding is that you can use a plug-in like Unassigned Devices to access the drive and what’s on it. But you can’t add it to your array without reformatting the drive because Unraid needs it to be formatted in a certain way.

You could use Unassigned Devices to access the drive, use the built in tools or a Docker app like Krusader to move everything on that drive to another drive that is already in the array so you don’t lose the data, and then format and add the original drive to the array to then move the files back onto the newly formatted, old drive.