Instead of overthinking what I haven't achieved, I think about good things in my life such as: the happiness of a parent whose daughter's math score rose from 3.5 to 7 in my math class, or such as the thankfulness of my best friend when she gave me a small gift for helping her daughter to learn English. Gratitude becomes my focus when I avoid negative thoughts.
Use the structure: "overthink + NOUN". For example, "I overthink negative things".
To list the good things you have, identify them with precise nouns: the HAPPINESS of a parent, the THANKFULNESS of a friend.