<p>You click on "start a bounty" on an eligible question.  From the <a href="http://meta.stackexchange.com/questions/16065/how-does-the-bounty-system-work">bounty FAQ on MSO</a>: "A bounty can be started on a question two days after the question was asked."</p>

<p><img src="https://i.sstatic.net/Ah3Yi.png" alt="bounty"></p>

<p>As of this posting, your only <a href="http://serverfault.com/questions/274007/how-do-you-reboot-a-server-when-you-are-not-local-to-it">unanswered question</a> is 1 day old, and not eligible yet.</p>