The new Dark Theme is introduced on latest Tecno phone models that are running on HiOS 6, such as Tecno Camon 15, Tecno Camon 15 Pro, Tecno Camon 15 Air. The dark mode does not only reduce the screen’s irritation to the eyes in dim environments, but also saves energy and extends battery life effectively. Enabling the dark mode or theme on Tecno phone is just a breeze. Just follow the easy steps below.
Method 1. Enable dark theme from Settings
Open Settings, choose Display, you will then get a screen like this.

Touch the Dark theme toggle to turn it on or off. Once the dark mode is enabled, you will see the dark background and white text immediately. Run other system apps, stock apps and even third-party apps, you should see the dramatic change. Although the dark mode gives us great viewing experience especially in low-light environments. Not all apps support dark mode. Third-party apps need to be optimized to compatible with the dark them on our mobile phone.
Method 2. Turn on dark mode from Notification Drawer
You can also pull down the Notification Panel from the top of your Tecno phone. Above the Notification panel is the Quick Settings panel where you can find shortcuts to turn on or off system settings, such as Wi-Fi, Airplane mode, Bluetooth, Flashlight, screen rotation, etc. Find and touch Dark Theme to activate it.

This is not in tecno spark 4 smartphone, dark mode is not available in tecno spark 4 .pls help