In Box D, the control
number, you may not have anything in that box, if that is the case, just
leave it blank. If you are trying to import your W2 and don't have
anything in Box D and if its required for import, you will have to manually
enter your W2 instead.
See below for more
information about how to enter a control number in TurboTax.
https://ttlc.intuit.com/replies/4417180