One should understand Graha Dosha in a horoscope first.
A dosha is an affliction of graha(s) based on its position, lordship, dhristi and placement in nakshatra and other divisional charts.
The type of doshas are based on Dharma and Karma of the person, as per the horoscope.
The remedies for all graha doshas are as follows
Dridha - Hard to change karmas and fixed
Dridha-Adridha - Pyschological effort has to be made to remove
Adridha - Can be easily removed
The above can be judged from the karmas, namely Sanchita, Prarabdha, Kriyamana and Agami karmas.
Navamsa plays an important role in identifying above dharma-karma, as it is 9th from 11th amsa delineator.
With Graha Dhaanya, color and puja (mantra, yantra and tantra), the remedies can be performed.
Psychological behavioral changes do help in changing the bad karma, provided it is done with sincerity.
Hindus were doing it in a traditional, cultural, spiritual and socially, by way of Parihara, Pujas and donations to poor for good karma.
Parihara are a subtle Hindu way to ascertain oneself that something that which is preventing an event not happening, be removed.
Pujas by praying to the Lord restores the faith in oneself to achieve one’s goal.
Donations to poor to create balance of karma.
And when the time comes, the event fructifies with divine grace.