Trip Computer Settings - MPG vs Ltrs/100K

[EriCal]

After the 45k mi service by the dealer on my treasured 08 S6, the Trip Computer mileage read-out is in Liters/100km rather than miles/gallon!! The odometer and trip meter are still in miles.
I want to change the Trip Computer setting back to mpg but I can't find how.
The MMI has a function to change the odometer/trip meter between kilometers and miles, but doing so has no effect on the Trip Computer. It remains at Ltrs/100Km no matter what I do.
I spoke with service at the dealer and his response was the typical "bring it in", but this is not easily done for me.
Can anyone advise where/how the settings are changed for the Trip Computer??

Thanks, Eric