A "full reset" usually means a factory install - which would destory all your data. Is that what you were intending? If so, you can alternatively zero the disks by connecting them to a windows PC (perhaps with a USB->SATA adapter) using vendor diags (either seagate's seatools or WDC's lifeguard).
Or if you have a spare disk that is the same size (or smaller) than the drives in the NAS, you could do a fresh install on that disk, and then hot-insert the existing disks. You should see a "format" option when you add the first disk - and you will need to reformat it before it can be added to the array. You'd wait for the resync, and then replace the spare disk (formating again, waiting for resync).
