This is the gold standard. Navigate to the Downloads or Firmware section of your device’s brand. Use the search bar with “SP36811.5” or browse by product family.
Interrupting an automatic firmware update (e.g., power loss) can render the device unusable. The SP36811.5 image is often the recovery tool. Sp36811.5 Firmware Download
Some manufacturers allow downgrades; others do not. Check the release notes. If downgrading, you may need to use the recovery mode and force-flash the older .bin file. This is the gold standard