JSFiddle - React, Tailwind, and code Playground

HTML

<div class="list">
  <div class="txt">
    
  <div class="header">main header for list</div>
    
    <div class="txt">
       <div class="header">header1</div>
       <img class="img" src=""/>
       <div class="txt" > 1</div>
       <div class="txt" > 2</div>
       <div class="txt" > 3</div>
    </div>
  
    <div class="txt">
       <div class="header">header2</div>
       <img class="img" src=""/>
       <div class="txt" > 4</div>
       <div class="txt" > 5</div>
       <div class="txt" > 6</div>
    </div>


  </div>
</div>

JavaScript

var divClass = 'txt .txt div.txt:nth-child(3)';
for(var i = 0; i < 1; i++){
    var divHtml = $('.' + divClass).html();
    $('.' + divClass).remove();
    $('.txt .txt:nth-child(2)').prepend(divHtml);
}