You have two ways to do this:
1) either go with Xeno file browser to the "root" of the media you want to scan, tap three dots (the directory context menu) and select "Scan int Xeno database". This will load tag data once, if you add anything there you'll have to scan it again.
2) go to preferences, "Where's my music" and tap + in upper toolbar, then select proper service. This way xeno will update your network share anytime it rescans its media sources.
Note that Xeno will happily scan the main root (xeno:/ filesystem), which contains all possible services and all found UPnP and SMB nodes. I'm sure you don't want to do that!