Where do I input last years tax refund in this years tax return.

You do not enter last year's federal refund into this year's return.   If you itemized deductions on your 2023 federal return and received a state or local refund then you enter those refunds into 2024.   If you used standard deduction for 2023 you do not enter anything about refunds for 2023 into 2024.

As xmasbaby mentioned, if you itemized your deductions in 2023, your state refunds from a previous year may be taxable.  State refunds are generally reported on a Form 1099-G. When you enter them, TurboTax will figure out if they are taxable or not.  Even when your refund is taxable, it may not be the entire amount. It depends on how much the deduction affected your refund or tax bill in 2023.  

Where do I enter a 1099-G for a state or local tax refund?

@rtcooks1