Amir's redemption process possess several steps.
1. Shortly after Amir's betrayal of Hassan in Chapter 7, he frames Hassan as a thief so that Baba will fire Ali and force Ali and Hassan to leave. Amir chooses the sin of theft because he knows that Baba considers it the only sin; thus, he hides his new birthday watch and some money in Hassan's hut. His plan does not work quite the way he wants it to. Baba forgives Hassan and Ali, but they choose to leave willingly, making Amir feel even worse about what he has done. Years later on his way back to Kabul, Amir stays with Farid's brother and his family. Recognizing their hunger and need, Amir leaves behind money and his watch with Farid's family as a form of redemption for what he had done to Hassan.
2. Amir's most significant step in his redemption is first believing that he can redeem himself for what he did to Hassan and then traveling to Afghanistan to get Sohrab. At that point, he does not know that he will face Assef again, but when he does confront the bully and "fight" him for Sohrab, he is doing what he should have done years earlier for Hassan. This time he does not hide or back down.
3. Finally, at the novel's end, Amir runs the kite for Sohrab. He puts himself in the "servant's" position instead of lording his Pashtun, wealthy status over a Hazara. He takes the opportunity to do all that he can for Sohrab since he cannot do so for Hassan.