JSFiddle - React, Tailwind, and code Playground

HTML

<div class="clone_block">
  Name: <input type="text" class="name" name="items[0][name]" /><br />
  Amount: <input type="text" class="amount" name="items[0][amount]" /><br />
  <button class="delete">Delete</button>
</div>

 <div class="clone_block">
  Name: <input type="text" class="name" name="items[0][name]" /><br />
  Amount: <input type="text" class="amount" name="items[0][amount]" /><br />
  <button class="delete">Delete</button>
</div>

 <div class="clone_block">
  Name: <input type="text" class="name" name="items[0][name]" /><br />
  Amount: <input type="text" class="amount" name="items[0][amount]" /><br />
  <button class="delete">Delete</button>
</div>

JavaScript

function renumber_blocks() {
    $(".clone_block").each(function(index) {
        var prefix = "items[" + index + "]";
        $(this).find("input").each(function() {
           this.name = this.name.replace(/items\[\d+\]/, prefix);   
        });
    });
}


renumber_blocks();