Android authentication using fingerprint

The flow of my applicaiton:

[1 -Login] -> [2 - Approve biometric use] -> [3 - Dashboard]

At the 2nd step, a user is authenticated and technically is inside of the app, enabling biometric. At this point, the user can click back button, Android standard keyboard. Is there an established pattern what should happen next?

My thoughts are the user should go back to [1 -Login] step with user name prefilled but password missing.