Open the device menu and locate the "Settings" option. It is usually represented by a gear or a cogwheel icon.

Tap on "Settings" to access the device settings menu.

Scroll down the settings menu and look for the "Biometrics and security" option. Tap on it to proceed.

Within the security settings, you will find various options and preferences related to device security.

Look for the "Install unknown apps" field or option.

To enable installation from unknown sources specify the source app that you will allow to install. In this case default web browser is Samsung internet, so by turning it on Samsung Internet will be allowed to install Mobile App not from the official app store.

A prompt or warning message may appear to inform you about the potential risks associated with installing apps from unknown sources. Read the information carefully and proceed only if you trust the source of the app you intend to install.

Once you have ticked the box, you can exit the settings menu by pressing the back or home button on your device.