ZR on serial output

I uploaded a compiled NET+OS 7.5 sample image via FTP to Connect ME DC-ME-01T-C. Now it just sends ZR on serial output when trying to boot, but doesn’t make anything more.

Is there any methods to recover this module? It doesn’t have JTAG.

Recovery instructions are here:
https://www.digi.com/support/knowledge-base/how-to-recover-a-digi-connect-wi-me-9210-wi-em-and