Can I change an answer to a question even if already filed and was rejected?

Yes, you can change things on your return if it is rejected.   Please read over this FAQ.    If you can't change your answer to NO in TurboTax, it is probably because the IRS believes you do have a 1095-A (or someone on your tax return) at www.healthcare.gov.    Verify you do not have one before attempting to use the workaround provided at the bottom.    

Use the workaround only if you are absolutely sure there is no 1095-A - and you will be able to e-file.   Heed the warning though - if it turns out you do have one and you don't enter it, your return's processing will be delayed.   

You probably have to file an amended return.  Wait until the return is accepted, then file an amended return. I am ot a tax professional, but have done my own taxes for 40* years.  You can read more about the 1095A here:

https://ttlc.intuit.com/community/credits-and-deductions/help/what-is-the-premium-tax-credit/00/26423

File an amended return with the correct answer.

If you said you had a form 1095-A but didn't enter anything from that form in TurboTax, then your tax return is probably correctly stated. You can prepare an amended return to see if your tax changes and if not, you don't need to file it.