In case anyone comes across this and has a similar issue, I found something which worked.
https://docs.exvist.com/hdmi-video-encoder/resources/faq/upgrade
I was able to get the firmware installed and the device working again.
@watkipet did you get any further with this one?
I have what appears to be a brovotech HDMI encoder which was bricked after an unsuccessful firmware update. I can telnet into it though and found the password to log in but I can't work out how I can try to re-flash the firmware.fw file to it...