The most efficient way to change settings of Galaxy S9 and S9+ is to use Galaxy S9 quick setting button.
This Galaxy S9 guide explains everything you need to know about the quick setting buttons on Galaxy S9 and S9+: what are Galaxy S9 quick setting buttons? How to access them, how to use them, and how to customize them.
Update: after you update Galaxy S9 or S9+ to Android Pie, you can use the night mode to set the background color of quick settings panel to dark. You can also use the quick setting button to switch between using the new Android Pie navigation gestures and using the traditional navigation bar/buttons.
What are quick setting buttons on Galaxy S9 and S9+?
The quick setting buttons allow you to instantly turn on or turn off some features quickly without entering the complicated settings page.
For example, you can turn on or turn off mobile data or Bluetooth using Galaxy S9 quick setting buttons on Galaxy S9 and S9+.
Since Android Nougat, stock Android also shows quick settings bar (the first a few quick setting buttons) in the notification panel, in addition to the full list of quick setting buttons.
But Samsung added the quick settings bar in Galaxy phones a long time back.
Anyway, quick setting buttons on Galaxy S9 and S9+ were designed to help you use the phone easily and efficiently.
The first 6 Galaxy S9 quick setting buttons (sometimes, it is referred to as quick settings bar) are shown above notifications in the notification panel as shown in this guide.
You can expand the list to show all quick settings buttons in Galaxy S9 notification panel.
How to access quick setting buttons on Galaxy S9 and S9+?
There are two methods to access all quick setting buttons on Galaxy S9 and S9+.