The Modular Face has a 'Settings' mode. To get to it, choose the Modular Face, then press and hold on the face. You'll see a miniaturized version of the face with the word Modular above it, and a button called 'Customize' below it. The miniaturized version will zoom out but with a frame around it. From there you can then swipe the frame to the left, revealing smaller frame around different zones on the face. You can swap in or out different information (weather, date, stocks, fitness rings, calm, etc.) to that it shows up in the different zone you choose to operate on.
It's hard to describe this without screenshots, but the key is to remember the long press on the Modular face, touch 'Customize' at the bottom, and then use combinations of touch and the crown (for navigating large lists, etc.)
Hope that helps.