Pico 4WD <-> esp8266 (esp12s) wsserver upgrade

following the docs on the official web site and on official gitub repository for the pico_4WD car, I would like to flash the new esp8266-uart-wsserver binary onto the esp-12s which is part of the pico RDP board.
According to the doc, in order to put the esp12 into download mode, we need to:
IO0 connect to GND, connect RST to GND and then hang after, esp8266 will enter download mode, generally esp8266 will flash quickly for a while.
For pico-4wd, you need to use a duplex cable to connect GND and IO0, then turn on the power,make the esp8266 enter the download mode, after that you can release IO0."

this is very unclear to me, which IO0 is it? relative to ESP12 or pico ? And which pin on the RDP is connected to the RST of the ESP12 ?
It would be nice if the documentation could include a figure of the links between the pico RDP pins, the esp12, pico itself and the available “signal” jumpers on the RDP.
Thanks for your help!

Please refer to the following link: