For severe bricking, desolder the 25Qxx SPI flash, flash it externally with a programmer, then reinstall.
M0422 OTA Firmware Changelogs!!! (Confirmed Via Chat Hisense) rsag7820 firmware download work
Sites like Elektrotanya provide service manuals and EEPROM/firmware files for specific board versions like the RSAG7.820.7924. For severe bricking, desolder the 25Qxx SPI flash,
C) Using dd or raw write (Linux/macOS)
If your TV isn't booting, follow these steps to force the board to read the USB: For severe bricking