If I received a 1095A for one month of marketplace coverage after I filed via TT, what do I need to do? I filed 1/29 and my federal return was accepted later that day

Check you original return to make sure you reported the 1095-A on the return. If you did, there is nothing you need to do. If you didn't then you will need to file an amended return. You should not try to amend your return until the original return it has been fully processed and you have received your refund or your payment has cleared.

Amended returns do not “catch up” to your original return and replace them; they are processed as two separate returns.  
Amended returns have to be printed and filed by mail.  It can take the IRS up to 12 weeks or longer to process them.   If you are due a larger refund than on your original return, your amended return should only show the difference and you will receive a separate check for it.  If you owe money on your amended return, it will show only the new amount owed, you will have to mail a check with the return. You can check the status of your amended return by clicking here: https://www.irs.gov/filing/individuals/amended-returns-form-1040-x-/wheres-my-amended-return-1

Thank you Will. I did not report on original return so I will amend once I receive refund. Will the absence of this form 1095A prevent me from receiving my refund? My WMR shows that my federal return was accepted and is in process.