The IRS does not require a control number on your W-2; it is there for the convenience of your employer.
If you can, just leave the control number field blank (or press Delete in the box).
If that doesn't work, please see this TurboTax FAQ for what to do when there is no control number on your W-2.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"