Enable USB Content Availability in the My Cloud Dashboard > Settings > General section. By doing so the attached USB hard drive should be included in the capacity chart on the Home page of the My Cloud Dashboard.
Example of a single bay first gen My Cloud with a 12 TB internal drive and a second 12 TB drive connected via USB.
One could “shuck” the WD Elements 3.5 inch hard drive and put it into the My Cloud enclosure using one of the various “unbrick” methods mentioned in this subforum. The above example image shows it being done with a similar WD external USB hard drive (from a WD EasyStore enclosure).
Another example here:
