This is very unlike say a PC.

Most folk call this "flashing the phone." I won't detail how to do this but your cell phone counters do it a lot and Garmin should be able to service the phone. You should not have been able to wipe out the OS on the phone by formatting it from the PC. I have another model of the Garmin phone and it can't be wiped out like this.

It also has no viruses I know of.
Bob