How to change menu item position

<?php
function repositionArrayElement(array &$array, $key, int $order): void
{
    if(($a = array_search($key, array_keys($array))) === false){
        return;
    }
    $p1 = array_splice($array, $a, 1);
    $p2 = array_splice($array, 0, $order);
    $array = array_merge($p2, $p1, $array);
}
repositionArrayElement($this->buttons, 'download', 1);
?>