1040x denied. Seeking help to understand the reason and advice how to proceed.

Had originally filed as single, but much later learned that if I support a parent I can file as head of household. I went through the flow of making changes on in turbotax online where I changed the filing status and filled in the new fields it asked. For the Part 3 "Explanation of Changes" I simply put something along the lines of "Changing file status as I'm adding a parent as a dependent". It generated a package which I signed as instructed and mailed everything. 

After 8 months I got back response saying that "You did not provide the form of name of the credit you are claiming on line 7. When resubmitting your claim, please include Form 1040-X, Amended U.S. Individual Income Tax Return, in addition to your supporting documentation." Looking at that Line 7 I see it changed from 0 to 500, but pretty sure this was done automatically by the software. I also see that some other fields have changed. I don't understand why they picked on this field or what they expect specifically for explanation or "name of credit".  Have a few questions to narrow down my next steps:

a) Did the software make a mistake? If this change required some technical explanation shouldn't the software fill it in or attach?

b) Is this some basic wording issue and I just need to copy paste some boilerplate explanation for this into Part 3 or was I supposed to provide some technical explanations for all the fields that changed?

c) If I can't figure this on my own, does turbotax have professional help service for amended returns that can help fill in the pieces here or do I need to seek help elsewhere?