This isn't the entire answer (TurboTax needs to provide that), but maybe this will help a bit. On the top left of the app, press the Forms icon/link. The screen will flip around and should take you to the item in question. I was able to determine what to fill in but imagine people's situations will vary. It wasn't super intuitive...
This error refers to the amount on line 5c of your Schedule A for 2018, which is state and local personal property taxes. That is usually the deductible amount of your vehicle registration fees.
If you did not itemize, you can enter 0. If you did itemize, just check your Schedule A from 2018 and fill in the number you had on line 5c.
**Mark the post that answers your question by clicking on "Mark as Best Answer"