Are you using a wireless network?
No you cannot reformat a single drive, the admin page does not facilitate that.
One word of caution, if you have a JBOD partition and either drive fails, you will lose access to the data in the JBOD volume, even if it's entirely contained in the remaining volume, also, assuming that you are correct and you do have a RAID1 partition, if a drive were to fail, and you replaced it, the system would rebuild the RAID array, but not the JBOD volume, so you'd end up with half of your disk space unutilized.
Just my $0.02, but the JBOD configuration on this devicehas no practical use - and the same goes for the RAID0.