Got IRS letter requesting documentation for Health Coverage Tax Credit (HCTC). Determined that I took HCTC by mistake. How do I respond to IRS?

Greetings,

 

I received an IRS letter requesting additional documentation concerning a Health Coverage Tax Credit (HCTC) I took on my recent income tax E-filing following what I understood from the TurboTax software I was using.  I have now researched this further and I now think I do not qualify for this credit.  I think I took this credit by mistake.  Becasue I was mistaken regarding HCTC, I simply do have the documentation they are requesting.  How should I respond to the IRS?