An Apogee Tech Support person may direct you to this article and video.
Note the special Duet3.bin file attached to this article.
This file is used to update Duet 3 firmware version to 1.0.4.
Use it as shown in this video:
Note: See this article on how to put Duet 3 into firmware update mode - Updating Apogee Duet 3 Firmware
And make sure you connect to the computer ONLY USING THE OUTSIDE USB-C port when performing the firmware update: