How To Vacant Someone From Brain

This battle is unwinnable.
See:
Ironic Process Theory
Thought Suppression
The Game

There is a LOT of literature on this subject. It should reassure to know that you are not alone in feeling this way! Such thoughts are the emotional/cognitive equivalent of earworms. The more you fight it, the more they will intrude. Two different strategies, among many, may be useful.

The first is to realize, really understand, that your brain cannot hold two thoughts at once. It may appear so, but what is actually going on is that you are switching rapidly from one thought to the next, but a great proportion of the thoughts are about whatever it is that you're trying to avoid. So, in order to reduce the proportion of unwanted thoughts, you might try working on some activity that requires focus and/or dexterity - preferably something physical that would engage both mind and body. For example, if you were learning to walk a tightrope stretched across a shallow pool (no fear of drowning, but definitely a danger of getting soaked!) then you will, more likely than not, be distracted from unwanted thoughts. So, perhaps you could try learning to juggle, to skate/rollerblade, or to play an instrument.

The second method is somewhat paradoxical. You learn to 'defang' intrusive thoughts by not avoiding or running away from them, but looking them squarely in the eye and paying attention to the physical correlates of thought and emotion. These could be sensations like a tightness in the stomach, palpitation, a sense of anxiety or dread, anger, fear, shallow/rapid breathing, etc. You notice them, see how they are connected to your thoughts, and try to stay with them - with the thoughts, emotions, feelings, bodily sensations - without trying to run away. You look them in the eye to see them for what they are - wisps of smoke. By allowing yourself to feel bad, you get better. These ideas are very well developed in Indian thought (Vedanā), and also in cognitive behavioral therapy. You can learn a lot from a little research. Good Luck!