If you manage to obtain an official update file (e.g., *.bin ), the process is straightforward. According to the Dutch manual, you need:
Click on the "Preparing your Radio" prompt. The tool will transmit the repack data to the device. Do not unplug the cable or turn off the device during this phase, as doing so can permanently break the unit. The radio will show a success message and reboot itself with the new Grundig logo sequence when complete. Troubleshooting Common Errors grundig sonoclock 890 web firmware update repack
Are you looking to to a specific unit, or are you trying to find a download link for a particular modified firmware? If you manage to obtain an official update file (e