Fix a Core Data problem in my iOS app

I've written a small fitness app which is a table view that will list all my clients. when you tap on the client you will see all their stats that you logged for them on day 1 of starting their 12 week program. On the client screen I have created a + button which allows you to enter their new stats every week and should save to allow us to view when clicking on the appropriate week button along the bottom. I have written all the code but need help as it is not functioning as expected. I am unable to edit or add the stats to my already created clients. Below is a screenshot of the app, If you feel you can resolve this small matter please get in touch