Only the society's leader themselves can appoint a new leader. Also, if a society leader has been absent from the game for a certain length of time, their role is automatically transferred to another player.
Here's how to pass on your leadership of a society to another player:
- in the society's chat section, tap on the "About the society" button
- select the player you want to assign as the new leader
- tap on the Promote button
- confirm your decision in the pop-up window.