One would need to find recovery software that supports accessing an NAS drive like the My Cloud. Perform an internet search to find such software. Or one can remove the hard drive from the My Cloud enclosure and attach it to a computer running Linux and attempt data recovery using Linux data recovery tools. Again perform an internet search for more information on how to recover data using Linux recovery tools.
There is also the following discussion that covers the possibility, at least on the second generation single bay My Cloud units running v2.x firmware, of installing a Linux program to the My Cloud to perform data recovery.
https://community.wd.com/t/wd-my-cloud-data-recovery/207487/
