The procedure to reach the System Settings menu will differ depending on what version of Android you have on your device, but one way you can always open this menu is by invoking the Apps list, whose icon is usually found on the main home screen.
Where is System menu on my phone?
To get to the menu, scroll all the way to the bottom of the settings screen. In the second-to-last spot, you’ll see a new System UI Tuner option, right above the About phone tab.
How do I find hidden settings on Android?
On the top-right corner, you should see a tiny settings gear. Press and hold that little icon for about five seconds to reveal the System UI Tuner. You will get a notification that says the hidden feature has been added to your settings once you let go of the gear icon.