For now all info on this subject is here

In order to restore the data from a snapshot, you replace the ncdata subvolume, as for example:

To remove datadir

sudo btrfs subvolume delete /media/USBdrive/ncdata

To restore old copy

sudo btrfs subvolume snapshot /media/USBdrive/ncp-snapshots/daily-xxxxx /media/USBdrive/ncdata

To update NC database with the new/old files