Manual Firmware download

I seem to have messed up a Q2400 by trying to download a hello world app. The OS version was 343 which I wanted to upgrade but wasn’t quite sure how. Regardless, the module now does not respond to “AT” or anything else for that matter. It echos the characters but does nothing except show +WIND 0 and 3 now and then.

How can I manually reflash the OS or otherwise fix it?

It was the wrong OS version for the OpenAT version used.