where can i specify overpayment to carryforwad as credit for next year?

To add, change or delete a current year federal tax refund to next year's taxes before you file your tax return -

Click on Federal Taxes (Personal using Home and Business)
Click on Other Tax Situations
Under Additional Tax Payments
On Apply Refund to Next Year, click on the start or update button

Or enter apply federal refund to next year in the Search box located in the upper right of the program screen. Click on Jump to apply federal refund to next year

The amount applied to next years taxes will be shown on Form 1040 Line 36

Yes, you can apply your 2024 tax refund to your taxes for next year.  Refer to the TurboTax Help article How do I apply my refund to next year's (2025) taxes? for detailed instructions for TurboTax Online, TurboTax Desktop, and TurboTax Mobile App.

You can apply your state refund to next year's taxes in the state return section.

1.  Select edit next to Other Situations 
2. Select Start next to Apply Refund to Next year
3. Enter the amount of your refund that you want to apply to your 2025 taxes.