First of all, you need to meet the following conditions to exile the Lord;

1; You must be a self-reliant king.

2; You must win at least one pub NPC, that is, a famous NPC with a surname, and then enter your own capital, the first captured city, find the chief minister and let the pub NPC act as a pawn.

3; After leaving the castle, the chief minister became the NPC of the pub and told him that I would exile a Lord in the name of treason.