In the Fitwill app you have an option to permanently delete your account with all your custom workouts and custom exercises. 

To permanently delete your account:

1.  Sign in in the app with your Google, Facebook, or Apple account 
2.  Tap your profile icon in the lower right corner of the screen 
3. Scroll to the bottom and tap “Delete My Account”
4. Type FITWILL in the text input to confirm
5. Tap “Permanently Delete My Account” button