From the readme file of Tinker Edge T OS zip file...
If you get unlucky and you can't even boot your board into the fastboot mode, then you can recover the system by booting into the fastboot mode from an image on the SD card and then reflash the board from your host computer as follows.
1. Power off the board and change the boot mode switches to boot from SD card.
(ON: Switch 1/Switch 3/Switch 4; OFF: Switch 2)
2. Use a program such as balenaEtcher to flash the recovery.img file to your microSD card.
Note: The recovery.img file is just the U-Boot image. Use that to recover a failing device by flashing it to an SD card and booting from that.
3. Connect the USB Type-C cable to the USB Type-C port on the board and your host computer.
4. Insert the SD card and then power on the board and the board should automatically boots into the fastboot mode.
5. Run the flash.cmd script for Windows or flash.sh for Linux in this directory.
6. When flashing is complete, your board will reboot. However, because you set the boot mode to SD card, you will see the fastboot mode again. So power off the board and reset the boot switches to eMMC mode.
README.txt
