if (isset($_GET['del'])) {
$id = $_GET['del'];
mysqli_query($db, "DELETE FROM info WHERE id=$id");
$_SESSION['message'] = "Address deleted!";
header('location: index.php');
}
<button class="btn" type="submit" name="save" >Save</button>
// ...
<body>
<?php if (isset($_SESSION['message'])): ?>
<div class="msg">
<?php
echo $_SESSION['message'];
unset($_SESSION['message']);
?>
</div>
<?php endif ?>