I meet people all the time who say, I know God has forgiven me, but I'm having a hard time forgiving myself. You might be saying this right now.
If so, you are not alone.
I wish I could point you to a specific place in the Bible that teaches self-forgiveness. But it's not there.
What is there is the forgiveness you have in Christ. God forgave you and to released you from your debt of sin. That's grace.
As CS Lewis said, I think that if God forgives us, we must forgive ourselves.
God's forgiveness is the truth that will set you free from your past and release you from your guilt and shame.
Are you willing to thank God for the forgiveness that you have in Christ today? It is the key to forgiving yourself.