The software will be updated using the service tool. You will need access to the rear of the TV for this so it will have to come off anyway.
I can't see why he requires the s/n because it should be selected from the software on the engineers laptop.
Having said that, the serial number will be 8 digits long (iirc) and can definitely be found under monitor settings in the service menu (again, 'iirc' - It's been a while... :) )