The single bay/single drive My Cloud models do not officially support third party modules like the more expensive multi bay My Cloud models do. It may be possible if one has the second gen v2.xx single bay My Cloud to enable third party apps but this is not supported by WD. See the following discussion:
https://community.wd.com/t/wd-mycloud-gen2-enable-apps-install-tab-apps/177885/
WD has a number of knowledgebase articles on using the Milestone Arcus with the My Cloud. Perhaps one of those articles holds the information you seek.
