Download stock firmware for NUM-200S Numcast TV Dongle from here, here or here. Perhaps it is possible to flash it using this method.
Firmware: Num-200S-sharing_20140526-3.0-rc3
Archive size: 13,6 MB
Image file name: Num-200S-sharing_20140526-3.0-rc3.img
Firmware: Num-200S-sharing_20140526-3.0-rc3
Archive size: 13,6 MB
Image file name: Num-200S-sharing_20140526-3.0-rc3.img