You can either skip that section and leave it blank. Or if you are receiving an error, just put in any combination of numbers in this specific format 5 digits, space, 5 digits (for example, 12345 67890).
That is just a number that the payroll team uses to identify your W-2 for their system purposes.This is not something the IRS needs, so as long as you input something in this format, you can proceed.