From Braiins Docs:
Users don’t typically have to enter recovery mode while using Braiins OS in a standard way. The restore2factory.py downgrade process uses it to restore the original factory firmware from the manufacturer. It can also be useful when repairing/investigating the currently installed system.
The recovery mode can be invoked in different ways:
IP SET button - hold it for 3s until green LED flashes
SD card - first partition with FAT contains file uEnv.txt with a line recovery=yes
miner utility - call miner run_recovery from the miner’s command line
Also:
If anything goes wrong and your device seems unbootable, you can use the previously created SD card image to recover original firmware from the manufacturer:
Follow the steps in Creating Bootable SD Card Image to boot the device
Run (on Windows, use python command instead of python3):
cd braiins-os_am1-s9_ssh_VERSION
python3 restore2factory.py backup/2ce9c4aab53c-2018-09-19/ your-miner-hostname-or-ip