First, you will have to acquire the TurboTax desktop software for 2018 to amend your return. To learn more information on how to amend your return, please see this TurboTax FAQ.
When you open your return to amend it, you perhaps will have to "add another state" (of course, you won't - this is just to get TurboTax to start the amendment process).
When you get back to the Virginia interview, go through the interview until you see a screen that says "Take a look at Virginia Credits and Taxes".
Under the subheading "Personal home and family credits", you will see a line item for "Neighborhood Assistant Act". Click "Start" to the right and tell TurboTax how much credit your received.