There is no definitive answer to this question since every pro player has their own preferences when it comes to Fortnite settings. However, there are some general setting tweaking tips that many pro players use which can help you get an edge on the competition.
One of the most important things you can do to improve your Fortnite gameplay is to make sure your game is running at a smooth framerate. If your game is choppy or lagging, it will be much harder to aim and build accurately. A good rule of thumb is to set your video settings to "Low" or "Medium" if you are having framerate issues. You can always adjust other settings after you have your framerate locked down.
Another common setting adjustment that pro players make is to change their Fortnite sensitivity. Depending on what kind of mouse you are using, you may need to experiment with different sensitivity settings to find what works best for you. Many pro players also use macro keys to bind their building keys to one button, which can help you build structures faster in the heat of battle.
If you are serious about improving your Fortnite skills, then you should definitely consider changing some of your in-game settings. Experiment with different settings and see what works best for you. There is no magic formula for the perfect Fortnite settings, so it will take some trial and error to find what works best for you.