Serial flashing the device with Tasmotizer
Carefully solder wires to ESP8266 chip and connect to appropriate pins on USB-to-TTL converter:
Do not use 5V! It will damage the chip.
Then connect another wire to GND and manually hold it on GPIO0 pin, then connect USB adapter to computer:
Device is ready in the flash mode and you can easily flash it with Tasmotizer. After that, gently unsolder the wires.