Synchro with external to Mac usb disc

Hi, I can’t synchro with My Cloud Duo external WD Passport I use as main disc for my Mac due to low capacity of internal one. In Finder there is no option to synchronize. What to do?

My Cloud Home allows to import data files from My Passport External USB drive but not sync. You can sync data files stored in Windows/macOS computer on My Cloud Home. For further details, follow below article: