When you visit Help Center > Privileges > Vote Up and Vote Down, you can read
You have a limited number of votes per day, use them wisely.
It is better not to vote when you are not sure about the usefulness of any Meta post so that you don't have to think about undoing your vote. If we know we can undo our vote whenever we want, we will more likely spend less time judging the quality of a post before casting a vote. As long as we are more careful when voting, we don't need to undo our vote. But if you really want to cancel or reverse your vote,
You can leave a comment requesting the OP edit the post so that you
can reverse your vote.
You can wait until an edit is made.
Should there be no edit, there is nothing we can do about it but move on. A lesson learned.