Expired tax credit and now has been reactivated thru the end of 2019. How do I file to get the $300 on an amended return?

I purchased a new central air conditioner and just got notification that an expired (in 2017) was reactivated and I could now get a $300 credit for the system on my taxes. How do I amend my taxes to apply for this credit? I have looked and see no way to input and get it in Turbo Tax.