If you have already filed your tax return you need to first wait and see if your return is accepted or rejected. If rejected, you can go back and make the correction by returning to the Health Care section and noting that you had health coverage all year then re-submit your return.
If accepted, you need to wait until you receive your tax refund and then Amend your tax return using the Amendment Form 1040X.
Here is an FAQ with additional instructions on Amending your 2016 tax return
https://ttlc.intuit.com/replies/5114064
