Ummm this is an oversimplified solution to a complexity. Overthinking is not a conscious choice. It is sub-conscious snowballing of repressed emotions/ residual stresses/ regretted inactions/ etc. "I should have said this... why didnt I", "I must confront her the next time... but what if"... and so on!
To work on overthinking, one must work on this - Do, say, express whatever you feel at the time and don't hold back. This is not easy but it will help reduce a lot of residual bs. 