How do we ask for forgiveness and to forgive someone in our past who has done us so wrong?
It is always good to start with humility. When asking God to forgive you or help you forgive someone who has wronged you, it always helps to remember that you yourself are far from perfect and you have wronged others just as others have wronged you.
Luke 17:3-4 is also a good passage to keep in mind. In these verses Jesus commands us to forgive on the condition of repentance. Even if the wrongs are continually done and yet are still continually accompanied by repentance, forgiveness is required. This would also mean that forgiveness would not be required if the wrongdoer does not repent. After all, God himself has never forgiven anyone who has not first repented.
With that said, it must also be pointed out that God shows love and kindness even to those who are unrepentantly evil (Matt. 5:44-45), and we are called to be like him in this way (Matt. 5:46-48). Thus, one should not think, “Ah, he has wronged me and he has not repented! That means I don’t have to forgive him! And THAT means I am allowed to hate him and treat him terribly!” No, even without forgiveness you are still required to love your enemies, bless them, and be kind to them (Matt. 5:44). After all, that’s what God did to you when you were still his enemy. Aren’t you glad he offered you his hand even while you were still in your sins (Rom. 5:6-8)?