It depends. You only need to include the State Income Tax Refund reported to you on Form 1099-G if you Itemized your deductions on Schedule A for the tax year you received the refund for.
For example, if your Form 1099-G shows a 2017 State refund of $100 and you Itemized your deductions on Schedule A in 2017, you will need to report this as income on your 2018 Tax Return. However, if you used the Standard Deduction in 2017, you do not need to report this as income and can just disregard the form.
If you did Itemize and need to Amend your return, you can click here for instructions: How to Change a Tax Return You Already Filed. TurboTax will walk you through Amending your State Tax as well.
The 2018 Form 1040-X is estimated to be available February 14, 2019. You can click here for information on IRS Forms Availability.
Note: You SHOULD NOT make any changes on your return in TurboTax until this form becomes available.
