Update :

include 'connect.php';
$id = $_GET['updateid'];
$sql = "select * from `user` where id=$id";
$result = mysqli_query($conn,$sql);
$row = mysqli_fetch_assoc($result);
$name = $row['name'];
$email =$row['email'];
$mobile =$row['mobile'];
$password =$row['password'];

if(isset($_POST['submit'])){
$name=$_POST['name'];
$email=$_POST['email'];
$mobile=$_POST['mobile'];
$password=$_POST['password'];

$sql = "update `user` set id= $id,name='$name',email='$email',mobile='$mobile',password='$password' where id=$id";
$result=(mysqli_query($conn,$sql));
if($result){
// echo "data updated successfully";
header('location:display.php');
}else{
die (mysqli_connect_error($conn));
}
}

?>

>>>in html coding
value="">

Display data:

include 'connect.php';
?>

>>in html coding

Add User

$sql = "select * from `user`";
$result = mysqli_query($conn, $sql);
if ($result) {
while ($row = mysqli_fetch_assoc($result)) {
$id = $row['id'];
$name = $row['name'];
$email = $row['email'];
$mobile = $row['mobile'];
$password = $row['password'];

echo '

';
}
}

?>