Thanks for using TurboTax
A Control Number (Box D) is used by many payroll departments to uniquely identify a W-2 in their system. If your W-2 doesn't have one, it's no big deal – you can simply leave it blank.
you get errors when attempting to e-file with an empty Box D, just
enter any number in this
format: 5 digits, space, 5 digits (for example, 12345 67890).
The IRS doesn't care what's in Box D because its use by payroll departments is optional.
Related Thread: https://ttlc.intuit.com/questions/2655867-box-d-matches-what-s-the-problem?jump_to=answer_4421994
Hope this helps