Similar to my previous post on the BSD29 Smart Plug the Girier wall switch have also been updated and cannot be flashed using an OTA method like Tuya-Convert due to an update in the PSK used. You can read more about the issue here. The only way to flash newer devices as for today (8 July 2020) is to flash them physically.

These are the necessary pins required for flashing:

• Red: 3.3v
• Blue: RX
• Yellow: TX
• Pink: GPIO 0
• Green: Ground

Check out Tasmota guide for more details on flashing.