How to turn TB-96AIoT into Maskrom mode when linux kernel boot failed


I bought and am trying TB-96AIoT and 96Boards SoM Carrier Board.
I successfully installed and booted linux.
After that I replaced rootfs with Debian’s one from Rockchip Linux SDK and it caused the boot to fail.

I tried to retrieve the original boot image but failed.

  • The board cannot be detected by lsusb, adb, and LinuxUpgradeTool.
  • I cannot enter to U-boot prompt with hitting Enter key repeatedly.

I think the board is not in Maskrom mode.
Could you tell me how to turn the board in to the mode, or how to use another boot source such as SD?

Here is my develop environment :

  • OS : Ubuntu18.04 LTS
  • CPU : AMD Ryzen 3 3200G
  • MEMORY : 8 GB

Thank you, all

This is solved by myself.
I found button on TB-96AIoT SOM.

Thank you.