Overthinking has been a big problem in most of the peoples life. Gives you a negative attitude, affects your relations with friends, family etc. How can you possibly stop yourself from overthinking when probably you have no control of what to think?
I personally say that I'm an over-thinker even my the ideas that comes in my mind I overthink whether that is beneficial or not for me. But What I did is i meditate and relax myself in that case it lessen my thinking. It is like refreshing your owns mind.