To view your old notification on Android, you have to do a small trick. This is by just adding a settings widget to your home screen, and making it a shortcut for viewing your old notifications. The below tutorial will let you know how it is.

How to View your Old Notifications on Android

  1. Go to app drawer and select Widgets tab.
  2. From available widgets, select “1×1 Settings Shortcut” widget and place it on your Home Screen.
  3. It’ll ask a function for your shortcut. Select “Notifications” from the available choices.

Now, go back to your Home screen and touch the newly placed Settings icon. It’ll display all your notifications. That’s all! [source]