On the evening of that day, the first day of the week, Jesus showed himself to his apostles. He breathed on them and said to them: "Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained" (John 20:19, 22-23).
The forgiveness of sins committed after Baptism is conferred by a particular sacrament called the sacrament of conversion, confession, penance, or reconciliation. To return to communion with God after having lost it through sin is a process born of the grace of God who is rich in mercy and solicitous for the salvation of men and women. One must ask for this precious gift for oneself and for others.