It took me a minute to figure out with fido my account app on iphone how to sign out of app, go to more at bottom right of screen,
click more, click settings on next screen,
settings is underneath your name on this page, click arrow beside logout to logout
There are no dumb questions!
I assume you're referring to the My Account app. Are you sure you're actually logged-in on the app? I'm not sure about the iOS version, but with the android version, the app can provide usage information without the need to log in. I'm guessing the app uses the phone number of the device to provide that information. However, in order to view billing information or to make changes, you are then required to log in. In my experience, once logged-in, closing the app automatically logs out of the app.
Hope this helps 😀