Yes, go ahead and delete the 2019 amount from your 2020 return, since you never claimed a credit for the windows. Leaving it won’t necessarily make the government think you received the credit, but it will make TurboTax think you did, and might import that information into next year’s return.
You might also consider amending your 2019 return to claim the credit for that tax year. Please see the 2019 Instructions for Form 5695 and the TurboTax Help article How to amend (change or correct) a return you already filed for more information.
