You cannot change the amounts on the 1095-A. You have to enter it as-is. Form 1095-A does not show the amount that the person paid out of pocket, so there is nothing to adjust for a difference in out-of-pocket payments. If Covered California did not adjust the advance premium tax credit, then showing the same amount of advance PTC for all 12 months is accurate. If they should have adjusted it, but didn't do so, you have to report the unadjusted amount.
