Thanks to @HikariCalyx for the helping me unlock the Pixel Watch 2 Demo device bootloader.

So I can change bootmode from demo(retail)to normal.

Because of the set_config command, it's need unlock bootloader first, but when you're in retail mode, you can't go into "Developer Options", so you can't enable "OEM unlock".
This caused me to be unable to unlock the bootloader.
Trapped in an endless loop.

For Chinese guide:
https://bluehomewu.github.io/posts/Pixel-Watch-2-Convert-Demo-Unit-to-normal-Firmware/

Fingerprint sensor calibration completed