Hmmm… This is what I got by email from support@gl-inet.com:
"You will have to set the unit into uboot mode first to load the firmware file.
To get into uboot then[ follow the instructions listed here. ](https://docs.gl-inet.com/en/3/troubleshooting/debrick/)
[You can also refer to the video found here. ](https://www.youtube.com/watch?v=EAaaw8nyrnE)"