I am very happy that you are interested in doing nyung-nä. It is great. Fantastic!
Nyung-nä does not just purify many eons of negative karma, especially developing compassion, which means bodhicitta, it makes us so much closer to enlightenment, so close to being able to enlighten all sentient beings, which is our ultimate goal in life. It also brings you closer to the Guru-Compassion Buddha.
As you chant more OM MANI PADME HUM mantras and generate more compassion for others, by doing one nyung-nä, you will be guided by Chenrezig in all lifetimes. By making one prayer to Chenrezig, you are guided in all future lives by the Compassionate Buddha, again and again. There is a story to illustrate this:
In the past, a person named Nyuktuk wandered in the intermediate state after death. He had lots of fear. Then, a white light came to him, and on the tip of the white light was an arya being. His right hand was in the mudra of giving sublime realizations and his left hand was holding the stem of a white lotus. He was adorned with scarves and jeweled ornaments, very holy and adorned, exemplified with marks and signs, and glowing. He descended in front of him and called to him: "Son, don't be afraid. I am Arya Compassionate One. I have come to guide you on the path." He said this directly from his holy mouth.
Then the hairs of Nyuktuk's body stood on end, tears fell from his eyes, devotion arose, he prostrated his head at the feet of Compassionate Buddha, and said: "Why have you come to such a pitiful being as me? What is the cause for you to guide me?"
Compassionate Buddha replied, "The cause is that in one of your past lives you were looking after an elephant that belonged to a king. You threw a baby elephant off a cliff. Due to that karmic result, in your next life you would have fallen down a cliff. At that time you made a request: ‘Please Compassion Buddha, understand.’ At that time I saved you from falling down the cliff. Since that time I've been guiding you in all your lifetimes. I guide anyone who makes just one request to me."
Every day, if you can recite OM MANI PADME HUM just one time, it stops you being reborn in the animal realm. If you recite it 100 times, it purifies the negative karma to be reborn in the lower realms. If you recite it 1,000 times a day, you will be reborn in the Pure Land of Amitabha Buddha. If you recite it 10,000 times a day, you will do extensive work for sentient beings.
In the past, a very foolish person who knew nothing of Dharma was looking after goats. He only knew how to recite OM MANI PADME HUM. When he died, a rainbow came out of the corpse and dissolved into the sky. He went to the Pure Land—Naro Kacho. Other people saw this happen. OM MANI PADME HUM naturally appeared on his skull, and it was worshipped by other virtuous friends.
Therefore, you are unbelievably fortunate to be able to practice nyung-nä. Your retreat is very important. You can dedicate the merits to the world and all living beings, for peace and happiness, to generate compassion, a good heart, and bodhicitta in all terrorists and violent people, in every person’s mind who has so much hatred for America and for themselves. Also, dedicate the merits to people who have the heavy karma to suffer from fire and other elements. So many animals have died in forest fires: ants, big and small beings. Pray for them. Perform nyung-näs for them. Perform nyung-näs for all the sick people, for all the people who are tortured, homeless, have no living and no job.