Obviously, Do Not Disturb (DND) does more than set brightness. It stops Alexa itself from disturbing you, and prevents incoming video calls from people you know who also have an Alexa-based device.
DND can be activated with a quick swipe down, or say "Alexa, activate do not disturb" or "Alexa, don't disturb me." The smart thing to do is schedule a regular set of DND hours. In the Alexa mobile app, go to Settings > Device Settings and find your Echo Show. Select the gear icon on the upper right, then Do Not Disturb > Scheduled. Set a start and end time. That'll keep callers from dropping in on you via Alexa during your off-hours, and dim the screen during that time as well.
Source : pcmag.com