See this TurboTax support FAQ for the procedure to use after receiving an IRS Letter 0012C for a Form 8962 - https://ttlc.intuit.com/questions/4348755-the-irs-is-requesting-form-8962-for-2017

1. Sign into your account with the same login you used when you filed your 2017 return.
2. Scroll down to the Your tax returns & documents section and select Amend (change) return, then select the Amend Using TurboTax Online box.
3. Select Continue on the We’ll help you change (amend) your return
4. Answer “Yes”, then select “I need to amend my 2017 return” and Continue.
5. On the We'll help you change (amend) your return screen, select the Federal Taxes tab. (Don’t select Continue. You don’t want to start the amend process.)
6. Select the Health Insurance tab.
7. Answer the questions about your health insurance which includes entering your 1095-A.
8. On the Do you need to change anything else screen select Done.
9. Select Tax Tools (found on the left panel), then select Print Center below it.
10. Choose Print, save, or preview this year’s return.
11. Select View or print.
12. Select Form 8962 and either Form 1040 or 1040A and print them.
13. Send the following to the IRS address or FAX number given in your IRS letter:
    • Form 8962, Premium Tax Credit
    • Copy of your Form 1095-A, Health Insurance Marketplace Statement
    • A copy of the IRS letter that you received.
    • Only if the refund or owed amount has changed: Also include page 2 of your 1040 or 1040A