In the case you set a bounty for your question and gave it to someone but after trying the accepted answer it did not work: how could you take back the bounty and let the question open again for a useful answer ?
That is not possible: All bounties are paid for up front and non-refundable under any circumstances.
- You should have checked the answer before awarding the bounty;
- You can flag the answer. That might get it deleted but the bounty is not going to return to you.