Officially there is no method for iTunes to access the My Cloud remotely. Generally for remote access one would use the MyCloud.comm web portal, FTP, WD My Cloud Desktop, WD Sync, or the WD mobile apps for iOS/Android.
There may be unofficial ways to enable iTunes access remotely but that may involve using SSH or setting up your own VPN network/connection. One possible way is to remote map the My Cloud using teh CloudDAVMod. Note this unofficial mod is for the older 1st generation v4.x firmware My Clouds.
https://community.wd.com/t/app-clouddavmod-various-versions-for-firmware-v4-09-2016/161543
There may be other options like using an alternate OS, do a forum search to find those threads.
