What do you suggest someone do to calm their brain when it races 24/7 with overthinking disorder?

I would suggest trying some guided meditation to get started. There are tons of videos on YouTube that can show you how to do it, and you will definitely be able to find one that you like. They have long and short ones so you can choose how much time you want to focus on it. I have also had clients tell me that just listening to music can be really helpful and calming.

I also like a technique called progressive muscle relaxation. It is where you tense a part of your body for 10 seconds and then relax it, making note of how you feel before and after. There is also a technique called biofeedback where you can be hooked up to a computer that shows your brainwaves. A therapist can help you look at your heartrate, skin temperature, and breathing. This can help show you what you are feeling like as you are triggered by something and help you figure out what to do to combat it.

If you are smoking or using a lot of caffeine, cutting those out could be a big help to you as well. Changing your diet to a healthier one can also have a positive affect on concentration.

Keeping a journal may also be helpful to you since it will allow you to keep better track of what you are thinking and how it is affecting you. Then you can go back and look at those journals to perhaps identify what some of the triggers are and how you can help combat them.

If you are having trouble sleeping because of this, it may be helpful for you to talk to your primary care doctor about it. Getting a good night's sleep can sometimes be a huge help in allowing someone to focus.