How can I change Drawer icon in flutter?

appBar: AppBar(
        leading: Builder(
          builder: (context) => IconButton(
            icon: Icon(Icons.menu_rounded),
            onPressed: () => Scaffold.of(context).openDrawer(),
          ),
        ),
        title: Text(
          "Track your Shipment",
        ),
      ),

You can open a drawer with a custom button like this too. create this scaffold key.

var scaffoldKey = GlobalKey<ScaffoldState>();

now added a scaffolled in your state class like this

      @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: scaffoldKey,
      drawer: Drawer(
        child: Text('create drawer widget tree here'),
      ),
      appBar: AppBar(
        backgroundColor: Colors.white,
        title: Text(
          'appName',
          style: Theme.of(context).textTheme.headline2,
        ),
        leading: IconButton(
          onPressed: () {
            scaffoldKey.currentState?.openDrawer();
          },
          icon: Image.asset(
            'assets/images/menu.png',
            fit: BoxFit.cover,
          ),
        ),
      ),
      body: Container(),
    );
  }

This should work.

Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title:Text('hi'),
        leading: IconButton(
          icon: Icon(Icons.accessible),
          onPressed: () => Scaffold.of(context).openDrawer(),
        ),
      ),
);

From the docs ->

{Widget leading} Type: Widget
A widget to display before the [title]. If this is null and [automaticallyImplyLeading] is set to true, the [AppBar] will imply an appropriate widget. For example, if the [AppBar] is in a [Scaffold] that also has a [Drawer], the [Scaffold] will fill this widget with an [IconButton] that opens the drawer (using [Icons.menu]). If there's no [Drawer] and the parent [Navigator] can go back, the [AppBar] will use a [BackButton] that calls [Navigator.maybePop]. The following code shows how the drawer button could be manually specified instead of relying on [automaticallyImplyLeading]:

import 'package:flutter/material.dart';
Widget build(context) {
  return AppBar(
    leading: Builder(
      builder: (BuildContext context) {
        return IconButton(
          icon: const Icon(Icons.menu),
          onPressed: () {
            Scaffold.of(context).openDrawer();
          },
          tooltip: MaterialLocalizations.of(context).openAppDrawerTooltip,
        );
      },
    ),
  );
}

The [Builder] is used in this example to ensure that the context refers to that part of the subtree. That way this code snippet can be used even inside the very code that is creating the [Scaffold] (in which case, without the [Builder], the context wouldn't be able to see the [Scaffold], since it would refer to an ancestor of that widget).