KC868-A4S for heating controll

[tadam]

these "rxd" and "txd" pin can be used. see photo.

Yes, yes, I understood that, thank you. But which pins are those on the esp32 itself?
I need two number for the setup. 
In esphome the setup should look like this in the code:
 "
opentherm:
     in_pin: GPIOXX
     out_pin: GPIOXX
"