Presumably it's similar to the calibration word in small PIC's?, as such it's stored inside the chip, placed there during testing at the factory. Your programmer 'should' automatically read and restore the calibration byte as you erase or write the chip - it's actual value will vary depending on the specific chip, that's why it's called a 'calibration' byte.
The datasheet for the device should tell you where it's stored, for PIC's it's the highest word in program memory.