You will find the input for the Maine Property Tax Fairness Credit in the state interview section of the program.
Once you start your amended return, you will proceed to the state interview section and answer the questions as prompted. You will eventually reach the credits section where the program will ask some questions to ensure you are eligible for the credit. If you are not eligible, the program will let you know. If you are eligible, the program will let you know and proceed to generate your state forms with the credit included.
In addition to the residency requirements, you also cannot file as married filing separately or exceed the income limits as show in the screenshot below from the 2023 Schedule PTFC/STFC instructions.