Sites like FirmwareFile provide stock ROMs in ZIP packages that include the flash file, a flash tool (like Miracle Tool), USB drivers, and a manual.
The code typically follows the nomenclature used by major chipset manufacturers (often HiSilicon or Ambarella) or assembly plants.
Before applying any update, export your current device settings (network parameters, logic programs, calibration data). Failure to do so may result in a factory reset and loss of work.
Do download from random file-sharing sites. Common official sources for such models: