If the TurboTax program is preventing you from continuing with (or e-filing) your return, you can leave Box 9 blank (this may require you to delete the Form W-2 and re-enter it in the W-2 interview - How do I delete forms in TurboTax Online?).
From the IRS article IRS Expands W-2 Verification Code for Filing Season 2018:
https://ttlc.intuit.com/replies/6494937
