How do i stop preservation on thoughts from my past?

Obsessive Thoughts: If you continue to think of the past there is probably something in your past life that is not resolved in your mind. Confide in a close friend and try to uncover the reasons for these repetitive thoughts. If you don;t regain relief consult with a mental health professional who can help you understand how to resolve past issues in your life. Best.

Find...: Find a hobby or ther distraction exercise. Place those thoughts in your own lock box...Not forgetting but allowing for healing and, growth from those thoughts.

Take your thoughts: Captive. Every time you stop that thought, and start a new one in another direction, you make a new path for your thoughts to travel on. Dirt road eventually becomes a highway that you like traveling. That happens with time. Like learning a backhand in tennis. Repetition key develops muscle memory. Eventually a reflex. Same with thoughts. Build yourself a new bridge. Good luck!

You can not stop it: Completely but you may decrease the intensity and frequency if it is very distressful and interfere with your day to day life . The best approach would be self practice of diversion /distraction when the unwanted memory or thought comes . The other practical step is what is termed as 'thought stoppage' . You try to stop it actively . By repeatedly practicing you can succeed.

Talk therapy: A good therapist might be able to help get beyond the issues/thoughts from the past with both cognitive/behavioral techniques as well as interpretation. It may take courage, effort & patience, but it can work.

See a therapist: It could be a symptom of many different disorders.You should see a psychiatrist for a consultation, find out what is this and get a professional recomendation.