JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="lista">
    <!-- preciso que o tem 1 vire o item 7, e o 7 vire o 1 -->
    <li class="prim">Item 1</li>
    <li class="prim">Item 2</li>
    <li class="prim">Item 4</li>
    <li class="prim">Item 5</li>
    <li class="prim">Item 6</li>
    <li class="prim">Item 7</li>
</ul>

JavaScript

var lis = document.querySelectorAll('ul.lista li');
var temp = lis[0].innerHTML
lis[0].innerHTML = lis[5].innerHTML;
lis[5].innerHTML = temp;