2nd Coming of Jesus: Has Jesus Already Come in Spirit? [To Ex-Shincheonji friends]

Shincheonji believes that Jesus came for the second time already, now working with a human being who is to be the messenger of God.
Does Christ need another person's to finish His work?
Does the Bible point to another person whom Jesus is going to work with, or Jesus Himself to come and finish His work?
What is the salvation plan of God in the Bible from the beginning to the end?