The Secret to Doing Real Teshuvah - No Matter How Bad the Sin
We find that anyone who kills another is exiled to the East, like Adam Harishon who caused death to all his descendents: “And he dwelt East of Gan Eden.”
And like with all the Cities of Refuge: “....across the Jordan, eastward....”
And so every killer hastens the setting of the sun of the one killed, as it says in Kohelet (12:2): "Before the Sun, the light, the Moon, and the stars darken...."
Therefore, he will be exiled to the farthest point from where he currently stands, like it says about Herod (Bava Batra 4): “He who extinguished the candle of the world should go and occupy himself with the light of the world.”
And this is the way of all baalei teshuvah: to incline toward the farthest point from the matter in which he sinned and to perform some mitzvah that is the opposite of the transgression he performed.
And this is the correct way for every baal teshuvah.
And the wise ones will understand from this Exile to repair every sin via a mitzvah that is the opposite of the transgression.
And through this, what has been corrupted will be repaired.
There is a tikkun for everything.
Furthermore, the Kli Yakar advises you to focus on a mitzvah that is the direct opposite of the sin committed. This is especially true for sins that cannot actually be repaired (like murder).
There is no need for despair or denial or wallowing. Just get moving "East."
This is my own translation and any errors are also mine.