If your Box 12 lines are blank simply skip it and move on to Box 13. If you believe that your W-2 is incorrect, you would need to reach out to your employer for assistance in obtaining a corrected W-2. Here's a TurboTax FAQ on filling out box 12 information from your W-2:
I got an extension on my taxes and decided to do it for free online on H&R Block and it won’t let me go forward until there’s something in there I’m confused
If you are going to use H&R Block instead of TurboTax then just clear your tax return and abandon the TurboTax account.
If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return. Click on Tax Tools on the left side of the program screen while working on the 2019 online tax return. Click on Clear & Start Over.
If I cancel my H&R tax return form bc I haven’t submitted it yet and did them throgh TurboTax free edition will I be able to skip over box 12 without a problem?
Yes, if there is nothing entered in box 12 on the W-2 you received from your employer, then there is nothing to enter on the TurboTax W-2 screen for box 12. If for some reason the TurboTax program gives you an error by not entering anything in box 12. Just delete the W-2 and re-enter to clear the error.
If you did not file your 2019 tax return with H&R Block then you can e-file the 2019 tax return using TurboTax.