The first step is to consciously notice the pattern - at first it may be difficult and you would notice it only after the fact, but with some introspection and training you can generally also learn to notice and acknowledge it while you're in it. When you do catch it with your "rational brain part" it's generally not that difficult to break it.

That's a big part of what cognitive behavioral therapy does. Also, mindfulness meditation is one way for doing this that helps some people with the "catch yourself doing that pattern" part.