Install unknown apps menu is changed on Android 8.0.0 (Oreo)

Symptom : Enable/Disable option is not showing on Android 8.0.0 version or Higher.

Cause : From Oreo, the setting was changed due to Google's policy. Previously, it was installed or not installed regardless of which app it was running on. However, currently, each individual apps asks if they want to install it.

Solution : 

1) Go to the path : SETTINGS > Biometrics and Security > Install unknown apps

2) Go to 'My Files'

3) Enable 'Allow From this source'

4) You will be able to proceed GDS Mobile/KDS installation.