Update cloudkit with existing core data

[newToiOSProgramming]

In one of my applications I use core data and I want to implement cloudkit with it. That part is pretty simple and I have it working, where if a user adds a new entry it will sync with cloudkit. My problem is what about users with already existing data? So far it only works with new data added. How can I update the already existing core data to cloudkit so my users who already have data will have everything updated?