Overthinking (26f) causing arguments (25m)

I have a bad habit of overthinking simple things then making assumptions. It doesn’t happen often (maybe once in a 4 month span) between my bf and I but when it does the arguments can get pretty intense. Our relationship is great but this is something I can work on to make it even better. What are some tips to help your brain slow down? Again this is something I am acknowledging I have to stop, what do you do when you find yourself overthinking?

Thank you for the respectful feedback :)