Understanding Automatic Login with Firebase Authentication

I created a login function using the Android app.
I use userid and password to log in.

After that, after the second time, I want to automatically log in without going through the login screen and transition to the main page, but I can't find a way.

I tried to implement automatic login using firebase authentication, but it ended up logging in via email and password.
So, how do I implement automatic login with userid and password?