source: SetUserAdmin.php

<?php

    if(!isset($_SESSION['user_ID']) || !isset($_SESSION['is_admin']) || !$_SESSION['is_admin']) {
        header("Location: ./Log In.php");
    }

    require "./connect.php";

    if(!isset($_GET['user_id'])) {
        header("location: ./Users.php");
        exit();
    }

    $res = $conn->query("SELECT * FROM users WHERE user_ID=".$_GET['user_id'].";");

    if($res->num_rows >= 1) {
        $conn->query('UPDATE users SET is_admin = 1 WHERE user_ID = '.$_GET["user_id"].';');
    }

    header("location: ./Users.php");
?>