title: How to update a specific(nth) child of a key in firebase
body: <p>I know that Firebase has some very basic query functionality with <strong>orderBy</strong>, <strong>limitTo</strong>, <strong>startAt</strong>, <strong>endAt</strong>...., etc. For updating has methods like <strong>update</strong>, <strong>set</strong>. In my case a i have an structure like this:</p>
  
  <p><a href="https://i.stack.imgur.com/0nfRZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0nfRZ.png" alt="enter image description here"></a></p>
  
  <p>So, there is a list of keys on my <strong>PIN</strong>, how can I update the child <strong>pin</strong> of a specific key with javascript?</p>
  
  <p>For example, I want now to update the <strong>pin</strong> of the second key. Now it has <strong>20</strong>, and I want to set it to <strong>30</strong>. But please, keep in mind that the list most have more than 2 keys, so maybe later I want to update the child <strong>pin</strong> of the fourth generated key.</p>
  
  <p>How can I do this?</p>