I have updated the tags for your post. Instructions are below.
After replacing the 6890A or Plus Mainboard, the serial number of the GC must be restored from the front panel. The 6890N Serial number can be restored from the front panel or via the GC Firmware Update Utility. To re-configure the GC serial number: 1. Press [Options], then select Diagnostics/Instrument Status. 2. Press [•] [•], 3. To change the numerical field, type in the GC serial number (shown below the GC keypad), and press [Enter]. 4. To change the country of manufacture, press [Mode/Type] after pressing [•] [•].