To increase the overall brightness of your Android TV's display, please follow the steps below.
Go to "DVB-T/T2" or any "HDMI" source by pressing the remote control's "Source" button
While on the relevant source, press the remote control's "Menu" button and go to "More". Select "Picture".
Select "Brightness" and "Contrast", and adjust them to your preference using the remote control's left and right buttons. Do note that changing the preset will automatically set the Picture Mode to "User".
Select "Gamma" and change it to "Bright"