Where does Turbotax allow me to list capital gains from the sale of U.S. Treasury bills for my Virginia return?

I sold some T-bills on the secondary bond market last year and had a capital gain from the sale.  Virginia does not tax capital gains from the sale of U.S. Government obligations, such as T-bills (see here: https://tax.virginia.gov/subtractions#obligations-of-the).  The instructions for VA Form 760 say these gains should be included in line 4 of Schedule ADJ so they can be subtracted from my income, but Turbotax does not allow me to change that line, nor does it ask for the information during the interview. 


Is there a way to add this data to my return without having to override Turbotax in the Forms mode? 


If not, why does Turbotax not ask for this information?  My tax will be higher if Turbotax forces me to ignore this aspect of Virginia tax law.