Log in to the web interface, go to Advanced, then click on Restore Configuration. On that page, you’ll see a button that says “Factory Default Restore.” Clicking that will go through the restore process, which puts it back to how it was when you took it out of the box. This will result in all data being lost.
But only for the 2 HDD Books, where the HDD can “easy” removed. But for the 1 Disk Version you have to do more effort. So you have to push 2 pins, which will to 99% break! On an warranty you will imho to send the whole NAS back to WD.