Question for Flashing an attached Microcontroller

[awatar100]

Hi, i have small problem or lack of full understanding how esp-link SW is working.
So i have Wemos D1 mini with esp-link connected to another Wemos D1mini (lets call it application uC) both are based on ESP8266. Standard functionality as uart to TCP / telnet is working OK. Reset GPIO is set to GPIO12 – works ok from web interface.
How can I flash application uC using eg esptool or Arduino IDE? I’v connecte ISP/Flash on web interface to GPIO5 of wemos that have esp-link -> this is soldered to GPIO0 for application uC. On my windows machine there is working com0com sw and virtual COM port created and configured. Now each time when I trry to use Arduino IDE or esptool flashing sw is not able to see application uC. So how esp-link set GPIO 0 to LOW state? Because as I understand GPIO 0 have to be in LOW to made flash procedure correctly (how this is activated ? on normal USB<>uart this pin is connected to RTS and DTR control pins)

Infor form esptool .:
esptool.py v4.8.1
Serial port COM42
Connecting......................................
A fatal error occurred: Failed to connect to Espressif device: No serial data received.

From Arduino ide .:
esptool.py v3.0
Serial port COM42
Connecting......................................_____
A fatal esptool.py error occurred: Failed to connect to ESP8266: Timed out waiting for packet header

How i can test flash GPIO that is set in web interface for application uC ?