I want to edit the button text inside this id "product_info"

Question

<div class="row">
  <div class="col-md-12">
    <div class="panel panel-default">
      <div class="panel-heading clearfix">
        <strong>
          <span class="glyphicon glyphicon-th"></span>
          <span>Add Sale</span>
       </strong>
      </div>
      <div class="panel-body">
        <form method="post" action="add_sale.php">
         <table class="table table-bordered">
           <thead>
            <th> Item </th>
            <th> Price </th>
            <th> Qty </th>
            <th> Total </th>
            <th> Date</th>
            <th> Action</th>
           </thead>
             <tbody id="product_info" > </tbody>
         </table>
       </form>
      </div>
    </div>
  </div>
</div>

I try to do script function still doesn't apply and changes the text of the button. Ive tried variety of codes just to change it but seems like all are not working.