For quick relief, stop and rest your eyes: look at something about 20 feet away for 20-30 seconds, blink slowly and fully several times to re-wet the surface, and close your eyes for a short break. A minute of this often takes the edge off.
Then remove the cause: turn the screen brightness down to match the room, cut glare, bump up the text size, and step away for a few minutes. Lubricating drops help if your eyes feel dry. For lasting relief, build the 20-20-20 rule and good brightness into your day, fast fixes work best when the strain isn't constantly rebuilding.
