We don't know. The state doesn't tell Turbo Tax anything. What did the state change on your return?
It just said tax and the year. I tried called but it’s all automated and got nowhere...grrrr
Well you have to ask them and find out. And be careful it might be a scam and not legit. Do you see that amount on your 2017 return somewhere? Check over your return especially the withholding and payments section. Like did you put down an extension payment or estimated payment you didn't make?
@VolvoGirl is right about the possibility of a scam. A legitimate letter from the Iowa tax department should contain lots of information, including contact information. See this: https://tax.iowa.gov/i-got-a-letter
I wouldn't send any money until you've verified things with the state.