Remind yourself that you are in control of what your hands are doing. Your hands are not doing this all by themselves. Enhance your awareness of what is happening. And decide to stop what you make your hands do. Develop the ability to tell yourself to stop (whatever the behaviour). If there is something pleasureable about the activity, try to analyze this, recognize this. Tell yourself to stop the behaviour. Think of the consequences of the behaviour - perhaps it affects your appearance. Think of some substitute behaviours - be able to change your activities. And congratulate yourself each step of the way. You can stop this behaviour.
There's Habit Reveral Traing (HRT) - (recognize and redirect) and cognitive-behavioural treatment.
All the best to you - you can overcome this.