Pictures

The Board:

The required pins are nicely labeled:

With attached DuPont wires, ready to access the flash:

How to access the flash (no soldering required):

• Power off the board
• Connect GND (black wire), TX (yellow wire), and RX (red wire) to your 3.3V UART TTL adapter.
• Short the two pins labeled BT and GND (green wires) just above the UART pins to keep the ESP32 in bootloader mode
• Power on the board
• You should now be able to use your ESP flashing tool of choice, like esptool.py (which is already available in your ESPHome venv)
• Backup the full flash contents and put it somewhere safe
• Write the initial ESPHome build
• Power off the board
• Remove the BT and GND connection
• Power on the board