In this question, there are multiple well-received answers.
The owner of the post chose the answer with -21 votes as the accepted answer.
The community seems to disagree.
What should be done?
Only the user who asked a question can accept an answer. A "community-accepted" feature is not currently planned.
If you believe the accepted answer is low quality, simply downvote it like you would any other answer.
To quote @JoeZ. "I'm sorry; this is a bad question given the answer you've accepted as correct". As the community cannot change the accepted answer, the question is as much of the issue as the answer and both deserve similar voting consideration.
There is nothing to be done, or should be done, this site is not centered around the community judging the validity of questions and/or answers, it's purpose is for people to ask a question, receive answers and then, themselves, choose the one, which they feel is the right one.
In most other subsites of the exchange that works well, although I, myself, have had a case where I would have liked to accept two different, yet equally fitting answers.
The "Puzzle" subsite is one of (or possibly the only?) exception, due to its nature. While it's idea is for puzzles to be posted and for users to have a bit of fun and mental exercise, the loose rules to which questions/puzzles have to abide by have lead it to become a section where questions of the sort of "what number am I thinking of" are dominant and as Bugs Bunny has so elegantly put it "Ask a stupid question - get a stupid answer.".
In effect nothing can be done about accepting the answer, without compromising the entire idea/ideal of the exchange, yet I think something could be done to improve the questions over at Puzzling.