Moderators cannot remove votes on posts, and don't know who voted for a post. Moderators can:

• Delete posts
• Convert an answer in a comment
• Convert a post in Community Wiki
• Convert a Community Wiki in a normal post (which will never become a Community Wiki anymore)

If there were more than one vote, they could be caught from the script against voting irregularities, and removed, but a single down-vote is not considered vote fraud.

If the down-vote would have been given because the wrong code, it should be removed once the code has been fixed. Down-votes are not a punishment for the user who posted, but they are given for bad posts, or the wrong information given in the post.
As the privilege page for voting down says:

Use your downvotes whenever you encounter an egregiously sloppy, no-effort-expended post, or an answer that is clearly and perhaps dangerously incorrect.

Moderators cannot remove votes on posts, and don't know who voted for a post. Moderators can:

• Delete posts
• Convert an answer in a comment
• Convert a post in Community Wiki
• Convert a Community Wiki in a normal post (which will never become a Community Wiki anymore)

If there were more than one vote, they could be caught from the script against voting irregularities, and removed, but a single down-vote is not considered vote fraud.

If the down-vote would have been given because the wrong code, it should be removed once the code has been fixed. Down-votes are not a punishment for the user who posted, but they are given for bad posts, or the wrong information given in the post.
As the privilege page for voting down says:

Use your downvotes whenever you encounter an egregiously sloppy, no-effort-expended post, or an answer that is clearly and perhaps dangerously incorrect.