<form id="ajax_form" action="" method="post">
</div>
<div class="modal-footer">
<button type="submit" id ="btn_edit" class="btn btn-primary">Сохранить</button>
</div>
</form>
$.ajax({
type: "GET",
url: "ds.php",
data: "id=" + id,
dataType: 'json',
success: function(data){
$("#ajax_form").html( $("#ajax_form").html()+'<div class="mb-3">'
+'<label for="recipient-name" class="col-form-label">ФИО:</label>'
+'<input type="text" name="fio" value='+data.fio+' class="form-control "
id="recipient-name"> </div>'
var elem = document.getElementById('form');