configure you ftp-server so that it (securely) allows access to nc’s datadir (this is completely independent of nc). use your ftp-client of choice (maybe one that supports mput -r) and transfer the files to the location you want them. take care that the files are owned by the webserver-user in the end. after that, run occ files scan (lookup exact syntax) to “register” the new files in nc’s db and transfer ownership to the desired nc-user.
GOOD LUCK!