My roku express keeps dimming. I checked online and I saw that you have to change brightness under tv picture in settings but roku express does not have this feature. Is there any other way to make it brighter?
Roku players don't have any display settings other than resolution and for 4K devices colorspace settings. Brightness settings are only available on the display you're using. Roku TVs would also have such settings of course.
I don't know exactly what you mean by screen dimming. The next time it dims, change your input to another device, or the TV tuner, and see if it is still dim. It's always possible your display (TV) is failing.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.