Yoga is not concerned with the question of evil and its solution in an absolute sense. The goal is mukti, or freedom, freedom from both good and evil. As Sri Ramakrishna says: One takes the thorn of knowledge to remove the thorn of ignorance, then throws both away.
For our purpose the illustration of a pendulum-clock is apt. When the pendulum swings to one side that very swing builds up the potential energy required to swing it to the other side. Both swings are equal and this swinging makes the clock work. If the pendulum does not work, the clock stops. Thus both forces of good and evil will keep the universe alive for us. If evil is to be transcended, the good will have to be abandoned too. For, as Swami Vivekananda has pointed out: Fetters, though of gold, are not less strong to bind.
A strong spirit of renunciation and unswerving practice, hold back the natural tendency of the mind to gush out through the senses. As we arrest the swinging pendulum by degrees, by curbing the wild transformations in the mind, it moves steadily towards the highest realm of human experience that is the result of the highest conscious control.
The yogi first puts a leash on thought waves related to the body like hunger, thirst, heat, cold, and sleep. Next, with the same leash (and method) the powerful internal instinctive energies like lust, greed, anger, hatred, jealousy and pride are brought under control. The negative side having come under the leash, it implies that the positive side also has come under control.