I want to change an old behaviour(worrying), but I don't know how?

Those small things were like tools to help you learn to live again. Now you no longer need those tools, you need others to move on to bigger things. When those thoughts occur, replace them with larger goals or things that are important to accomplish at this point in your life. Gently remind yourself you no longer need those thoughts to function. Something like, "I used to need to think of this, but I don't now. Now I need to think about _______." Give your mind something else to think about at those moments. Good luck, and congratulations on building your life back.