The first step is to figure out if it was an incorrect action or simply one you personally disagree with. If you are in a position to over-rule a moderator without them feeling slighted, then this doesn't really matter. If you are not, then discuss the action with the applicable moderator and reach a conclusion about the action in a way that won't cause problems amongst the moderation team itself.
If it is deemed that the action was in error, simply indicate that you disagreed with the action, you were not the one responsible, but you wish to protect the privacy of the person who is (unless it was severe enough of an issue to merit visible disciplinary action against the mod), and then reverse the action. Some users may still believe it was originally you, but if you aren't standing behind the action, most people will take you at your word. If you talked with the moderator and they also agreed with the reversal, it is probably worth mentioning that the original moderator is also on-board with the change.
If you are not able to come to an agreement without causing further issues within the moderator community, it may be best to let it be as a correct action you disagree with. You may want to consider getting another moderator to confirm you were not behind the decision (this is fairly safe to do as long as it doesn't give away who was actually responsible) or even to request that the actual moderator take responsibility for their action so that you don't have to take flack from the community on something you are in disagreement about.