How can you train your mind not to over-think?

I overthink a lot and it's horrible but I would say being aware that you are overthinking is crucial. Also don't focus on the negative things that can happen instead the positive things that could happen. Anxiety for example is fear of the unknown, once you understand that fully you will have much more control of the situation, why fear the unknown when we don't know what could happen. Remove yourself from negativity and remember that positive things could also happen :) Making yourself busy like having a hobby could help you forget about certain situations! I hope this helps :)