How to break obsessive thinking?

Many times I get into obsessive thinking loop where I start from one worry or issue that has to be handled to many more. Some times I realize I’m overthinking about stuff but many a times I get involved in this thought process and end up wasting time and energy. How to handle overthinking or obsessive thinking..I kinda feel my brain has got efficient on obsessively worrying about stuff and it defaults to that mode often.Its like even if I’m trying to focus on work the thoughts are running in background. I am not sure how to break this habit. How and where I do start ?