How to Address Negative Core Beliefs

I imagine there's a certain approach or methodology that goes into getting some of these obsessive behaviors to be lessened. Like what is the typical process? Send me in the context of health nutrition, training, etc. And so it sounds like because the chicken and the egg are both present, both arguably the chicken and both arguably the egg that you address both,. Is there a certain order? Do you try to address the negative core belief first, or do you try to kind of turn down the volume on those behaviors that are causing distress?"