Decoupling is a big fancy word that means separating two things from each other. In this case, we are talking about body-focused repetitive behaviors, which are things like biting your nails or picking at your skin. These behaviors happen when your body and your brain get stuck in a loop where you feel the urge to do the behavior, and then you do it over and over again.
To break this loop, we need to "decouple" the urge to do the behavior from actually doing it. This means finding a way to satisfy the urge without doing the behavior that harms your body. One method to do this is called "habit reversal training." This involves identifying when and where the behavior happens, as well as what triggers it.
Then, you learn to use a different behavior when you feel the urge to do the harmful one. For example, if you feel the urge to pick at your skin, you might instead clench your fists, squeeze a stress ball or take a deep breath.
Through practice, the new behavior becomes a new habit, so when you feel the urge to do the harmful behavior, you automatically do the new one instead. This decouples the urge from the harmful behavior and helps you break the cycle.