Overview button switches activity

I have 2 activities Activity A and Activity B. My app starts in Activity A and I have a button on Activity A that leads to Activity B. When I'm in Activity B, I press the Overview Button(The square button) and select my app. When my app loads up, Activity B is destroyed and it loads up into Activity A instead. What is going on and how do I get it to save my settings and load into Activity B?

By extension i'm having an app that loads into firebase authentication and then operates on a firebase database. How do I save the state of it when the overview button is pressed? Do I need to save anything with firebase authetication or do I just save all the data I need to access and manage the firebase database with that?

I watched a couple videos on it where they are talking about screen rotations and saving states, but there's little information about the overview button.

Thanks,
Reinaldo

What about saving the current activity to a value in shared preferences and then checking the value in the onCreate method of activity A. You can have a switch statement that redirects to whichever activity the user was on before.

activity A would look like this:

public class A extends AppCompatActivity {

private String currentActivity;
private final String CURRENT_ACT = "current activity";
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    SharedPreferences sharedPreferences = getSharedPreferences("shared preferences", MODE_PRIVATE);
    currentActivity = sharedPreferences.getString(CURRENT_ACT, "A");

    switch (currentActivity){
        case "A":
            break;

        case "B":
            Intent intent = new Intent(this, B.class);
            startActivity(intent);
            break;
    }

}

}

and B would look like this:

public class B extends AppCompatActivity {

private String currentActivity;
private final String CURRENT_ACT = "current activity";

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    currentActivity = "B";

    SharedPreferences sharedPreferences = getSharedPreferences("shared preferences", MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPreferences.edit();
    editor.putString(CURRENT_ACT,currentActivity);
    editor.commit();

}

}