You essentially prepare a new 1120S then make a list with the changes. In TurboTax Business, it is best if you start by opening your 2024 return, then going to the File menu and using the Save As... to have two separate tax return files. (and the original, if you just go in and start making changes, it is difficult to un-do them if you need to). There is an amended box you can indicate on the 1120S.