Hi
If you have an existing watch face that is missing the Customise button, you can resolve this by deleting the existing Photo watch face and adding a new one:
- With the screen awake, press firmly on the watch face, swipe left / right to your existing Photo watch face (if you have one), then swipe up on the preview to delete / trash it.
- To add a new one, next swipe left / right to the New watch face option, tap on the New button (+), scroll to the Photo watch face (using the Digital Crown) then tap on it to select it.
- Or open the Photos app on your watch, press firmly on your preferred photo, then tap on Create Watch Face.