I think you found a possibility there, the DFOTA method should work I think. If you don’t have a web or ftp server on hand I can help out on that or you also should be able to use a free github account for that purpose.
And my problems is that the darned modem does not work properly anyway, so getting it to go online via 4G is a distant goal, not an established possibility. It is WHY I need to do the update.
Does this mean that you are not able to get a connection up running at all?
I also searched a bit about the Quectel modem, bit annoying that all their which can be downloaded only available to “Premium Users”…
I found this PDF which offers a bit of information about how to update the firmware via USB: QuectelEC2526EC2126EC2020R20QFlashLinux26AndroidUserGuideV10.770967582.zip (782.4 KB) (can not upload a PDF so it’s a *.zip…).
Seems like there are USB drivers and a tool needed, maybe the guy who sent you the firmware could give you access to those. Still not sure if or how it’s possible to set the WIO board in a mode to actually get the needed USB access to the EC21 and this method seems to be far more complicated than the DFOTA method.