How do you move your capital in the game?

IIRC you open the city view window and there is a button in the lower part of the screen that says "Set as Capital". :hmm:

open the settlement scroll window, the 1 that shows you public order, income and pop growth. there is a button there

Open the settlement scroll. I believe there is a button in the bottom left corner that says "settlement details". Click on it. There, in the bottom left hand scroll, there is a button that says "Move capital to this city".