Thank you for the helpful comments. I am not sure anybody 'wants' to format their internal memory.

I had the Garmin connected to my laptop and tried to update the maps via garmin express. I got an error saying there is not enough room on the sd card. Instead of formatting the sd card I formatted the garmin internal memory. Yes I should have put the sd card directly in the laptop and disconnected the garmin so it couldn't happen but it was an easy mistake.

Surely there is a way of rebuilding the system files?