Official Standard Configuration
If using the stock kit with no modifications or just looking for a place to start, you can find the stock Duet/RepRapFirmware config on the RepRapFirmware-SD repo from E3D.
Note: The standard configuration (as of Dec 1, 2020) is for RepRapFirmware v2 which is what comes on the Duet 2 that ships with the ToolChanger. There is currently no official configuration for RepRapFirmware v3. Do not update the Duet 2 firmware unless you are prepared to either make the necessary modifications to the official config or use one of the unofficial configs listed below. Be aware that these configs are not intended for a stock ToolChanger in most cases and will require further modification to work with your specific machine setup.