Apart from karma, there is scope for free will (called “purushartha”) in human lives. Good action and good thought can reduce papa and increase punya. Whether free will or karma will prevail or to what extent free will can mitigate karma depends on the relative strength of the two. Since there is no way of knowing what one’s karma is, wisdom lies in doing good actions and entertaining good thoughts. One should not lose faith in the efficacy of good actions and good thoughts; good actions and good thoughts are bound to bring about a better balance of punya papa and, consequently, mitigate suffering and increase happiness in the present janma itself or in future janmas.
Brhadaranyaka Upanishad, fifth chapter, fourteenth section talks of the beneficial result of the chanting of the famous Savitri mantra in the Gayatri metre.
Full Article: Free Will according to Advaita Vedanta