Does my action constitute aiding in sin and necessitate expiation because I transported a blind man to a church?

Guiding a blind person is permissible before knowing their destination. However, once you know their intention is to go to a church, you are not permitted to help them in any way, because it falls under cooperating in sin. Allah Almighty says: "And do not cooperate in sin and aggression." Expiation for sin is achieved through sincere repentance, seeking forgiveness, and increasing good deeds.