[shaikh samiul islam]

Is there any app so i can manually low my display brightness

[P1ng0fDeath]

You don't need any apps, just go to Settings > System > Screen and disable automatic brightness there.

[pankaj981]

You could also pin the brightness control to the action center. Each tap will toggle between high, low and medium.

[P1ng0fDeath]

Depending on the phone you can also adjust each brightness level individually, using Brightness Profile. You can set Low to be as low as possible, for example.