Error message and check the fields

I created a form to update the data, after some difficulty I succeeded, but now I need to perform the necessary checks and enter the error messages or success. I tried this, but nothing happens:

//submit post
if (isset($_POST['email'], $_POST['location'], $_SESSION['username'])) {

    //query update
    $stmt = $db->prepare("UPDATE members SET email = ?, location = ? WHERE username = ?");
    $status = $stmt->execute([$_POST['email'], $_POST['location'], $_SESSION['username']]);
    if ($status) {
        echo 'It worked!';
    } else {
        echo 'It failed!';
    }

    //redirect to index page
    header('Location: account.php');
    exit;

} 

How can I improve it by adding the necessary checks of the fields etc., and insert the error messages and successful? thanks