A certain couple has filed their 2015 tax return and then they got a corrected 1099. The only thing that got changed was the amount of tax free interest they received. Since they are currently on medicare, they want to file for a correction. The only line that needs to change is line 8b on their 1040.
I am thinking they should file form 1040X but that form does not seem support changing the amount of tax free income they reported. What should they do?
Note: They live in the US