I can’t help I’m afraid. @glyn.hudson provided that binary file (3-phase in Austria - #31 by Robert.Wall), and I don’t have an ESP8266 so I’ve no idea what you need to do.
I’d start here: GitHub - openenergymonitor/EmonESP: ESP8266 WIFI serial to emoncms link (and there’s a link to that in the Guide).
There is a mention of Esptool.