You didn't say whether you are using TurboTax Online or the CD/Download TurboTax software. I assume you are using the CD/Download software. There is no way to enter the credit in TurboTax Online.
The only way that I can see to enter the credit is to use an override. It seems to work, but using an override cancels the TurboTax accuracy guarantee.
These instructions are for Windows. The procedure will be basically the same if you are using a Mac, but the details might be different.
You don't enter the credit directly on Form IT-201-ATT line 18. In forms mode, open Form IT-201-ATT. On line 12a click on the space for either Code or Amount, then click the little magnifying glass to QuickZoom to the Other Tax Credits and Taxes Worksheet. Scroll down to Section D of the worksheet and click on line 9, which is for IT-237. Make sure you are in Section D. There are other IT-237 entries in other sections of the worksheet. Either press Ctrl-D or right-click line 9 and click Override on the pop-up menu. Then you will be able to enter the amount of the credit on line 9. The amount will then appear on Form IT-201-ATT line 12, and it will be added in to line 13, and will be included in the total on line 18, which flows to IT-201 line 71.
