Hi there,
You can boot from sd card and then modify /boot/uEnv.txt to enable emmc flasher. When the flashing is complete, all 4 USRx LEDs will be off. The latest Debian flasher images automatically power down the board upon completion. This can take up to 10 minutes. Power-down your board, remove the SD card and apply power again to be complete. thanks.
</s>##enable BBB: eMMC Flasher:
cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh<e>