Health App Connect to Noom?

I am trying to connect my Health app to my Noom app so that it will sync track my steps and exercise. It should be fairly straightforward, but when I try to sign in to iHealth through the Noom app, it says I don't have an account. I don't think I ever set one up- it just came with the phone and is now synced to my Apple Watch, so I don't have any login information. How can I sync to this account (that is already connected to my watch) with the Noom app?