See this IRS website for information on IRS notice LTR0012C - https://www.irs.gov/individuals/understanding-your-letter-0012c
See this TurboTax support FAQ on the procedure to use concerning the IRS notice - https://ttlc.intuit.com/questions/3155571-what-do-i-do-if-i-received-an-irs-letter-about-a-missing-f...
