Update 2021/02/17 Tuya-convert OTA failed for this plug due to its factory loaded Tuya firmware (PSK identity 02).
This plug contains a TYWE2S.
To open the shell of the device the green rubber cap have to be pulled up and two tri-wing security screws have to be removed. To flash, wires have to be soldered to 3.3v, GND, TX, RX and GPI0(to GND). Remember to swap RX and TX on your FTDI board!
GPI0 sits just behind a capacitor that needs to be desoldered. Pinout (TYWE2S):