@Milke If you are on 3.1.1, the instructions say to update to 3.3, then a later version. Realistically, you don't need to; you can go from 3.1.1 direct to 3.4.6 (the current release version).
Download the 'Duet2and3Firmware-3.4.6.zip' from https://github.com/Duet3D/RepRapFirmware/releases/tag/3.4.6 Upload it to the Duet. As you are on 3.1.1, this will put all the firmware files in the /sys folder Let the Duet update the firmware Occasionally, updating the WiFi firmware fails, and you can't connect to the Duet. Connect using YAT via USB, and send M997 S1 P"0:/sys/DuetWiFiServer.bin" to update the WiFi firmware. Connect to the Duet via DWC. Check that the firmware and DWC are on version 3.4.6. Upload 'Duet2and3Firmware-3.4.6.zip' again. This will create the ‘0:/firmware/’ directory, and put all the firmware files in it. You can delete the firmware files from the /sys folder.Ian