https://github.com/xoseperez/espurna/wiki/Hardware-BLITZWOLF-BW-SHP2

Different to board on this page, mine has following markings:

HYS-01-008_V3.4
2018-07-20

Short GPIO0 and GND during boot to enter flash mode before connecting to the serial programmer. The power indicator LED will be strong red to confirm the device has entered this mode. As soon as the short is removed, the red color will be dimmed. The device will then be ready for flashing.

https://github.com/xoseperez/espurna/releases/tag/1.13.5

root@x200:/mnt/nuc/esptool# wget https://github.com/xoseperez/espurna/releases/download/1.13.5/espurna-1.13.5-blitzwolf-bwshpx.bin

root@x200:/mnt/nuc/esptool# ./esptool.py --chip esp8266 --port /dev/ttyUSB0 erase_flash
esptool.py v2.7-dev
Serial port /dev/ttyUSB0
Connecting....
Chip is ESP8266EX
Features: WiFi
MAC: 80:7d:3a:4e:32:97
Uploading stub...
Running stub...
Stub running...
Erasing flash (this may take a while)...
Chip erase completed successfully in 1.3s
Staying in bootloader.

# again power cycle device with gpio connected to ground, and disconnect it....

root@x200:/mnt/nuc/esptool# ./esptool.py --chip esp8266 --port /dev/ttyUSB0 write_flash --flash_mode dout 0x00000 ./espurna-1.13.5-blitzwolf-bwshpx.bin 
esptool.py v2.7-dev
Serial port /dev/ttyUSB0
Connecting....
Chip is ESP8266EX
Features: WiFi
MAC: 80:7d:3a:4e:32:97
Uploading stub...
Running stub...
Stub running...
Configuring flash size...
Auto-detected Flash size: 1MB
Compressed 492880 bytes to 352587...
Wrote 492880 bytes (352587 compressed) at 0x00000000 in 31.2 seconds (effective 126.5 kbit/s)...
Hash of data verified.

Leaving...
Staying in bootloader.