The IRS web site explains more about form
letter 0012C requesting more information about the 1095-A. That web site gives you a number to call (1-866-682-7451, extension 568) for more information, like the fax number or address to send your form.
See the FAQ below fore more information about how to respond to this letter.
https://ttlc.intuit.com/replies/5824742
