Overthinking comes from fear, and if we keep thinking about something we fear that hasn't happened yet, we are going to have hard time going through the day.
One of the biggest problems we have is always thinking about the negative outcome of a situation. If we can stop thinking about something bad that might happen, and think about the good that could happen, the situation itself becomes easier to handle.
The moment we begin to focus on the negative outcome, we become paralyzed from our thoughts. We have start flipping our perspective and start focusing on what good can we get out of whatever situation you are in.
At the end of the day, it's really about not letting yourself overthink so much about the negative in a situation, and become mindful of your thoughts.
Trying to find the positive everything is great thing for you to do and it will make your life so much easier.
If you do end up in a situation that you can't control, the best thing to can do is to let go, accept that it happened, and move on because life is constantly moving on with or without you.