Order custom Taxomony alphabetically and reversal after clicking a button?

Pass order parameter in url on click on link like /?order=DESC or if you are using a button then it must be submitting a form with order field value change GET to POST and field name

if(isset($_GET['order'])){
$order = $_GET['order'];
}
else{
$order="ASC";
}
$categories = get_terms( 'category', array(
'orderby'    => 'name',
'order'=> $order,
) );