I feel that a fathomless intelligence is within us. The more noise there is in my mind, the less intelligent I feel. The more peaceful my mind, the more I can access this intelligence. A mind that is consistently filled with many thoughts is a mind that is not peaceful, a kind of anxiety is there.
Meditation will teach you how to quiet your mind in a natural way. Start with this excellent article that explains how and why to practice meditation and how it helps create silence in your mind.
Practice meditation regularly for a while, and you will understand how to end overthinking.