How did Marley begin the process of Scrooge's changes in 'A Christmas Carol'?

Answer 1

He showed him aspects of the past, present, and future. He made Scrooge realize what was happening in the lives of his poor worker. He showed him (Scrooge) himself. He saw how cruel he was and what would happen if he did not change his ways. He saw too much and decided to change his and Tiny Tim's future.
To tell Scrooge his bad deed an wrong doings.

Answer 2

Marley's ghost visits Scrooge to warn him about the consequences of his selfishness and greed. Marley states that three spirits will visit Scrooge over the next three nights to show him the error of his ways and offer him a chance at redemption. This encounter with Marley serves as the catalyst for Scrooge's transformation throughout the story.