Today is a good day.
Whenever you are thinking about a bad thing that could happen, your brain is making it worse than everything that will happen. Stop overthinking.
Instead think about, what is the best possible outcome of the situation or what you could do to make the situation more enjoyable.
Sometimes you also need to get out of that situation. Then you need to replace your thoughts. You won't stop thinking about something if I tell you; Stop thinking about a red car. Now you think of a red car.
If I now tell you about having a cold beer at a beach on a small island and enjoying the sunset, you are probably thinking about that cold beer. You can do that with any beverage and every location.