There is no specific log out button. In order to log out of the app, you simply need to exit or close the app like you would any other app on your smartphone. If you have Pin access enabled, you will be required to enter the Pin in order to access the app next time you open it.
Even in regular use, if you navigate away from the app and then switch back, you will be required to enter the Pin to access the wallet.
So in essence when you exit the app, or navigate away from the app, the GoldPass system automatically pin locks you’re account, in the same manner another app may log you out.