If you have already created a FitSW account but want to begin using Sign In with Apple, this article will tell you how.
If your FitSW Login email already matches your Apple ID, you don't have to do anything extra. You can begin using Sign In with Apple now. If they don't match, follow the steps below in order to update your FitSW Login email to match your Apple ID.
1) Login to FitSW using your FitSW Login email (not using Sign In with Apple).
2) Go to the Profile page.
3) Click the Change Login Email Button
4) Change your Login Email to match your Apple ID.
5) Login with Apple will now work since your Apple ID and FitSW login match.