Why is Android Studio showing an error when I try to use setText() on a Button?

I'm making an app where I'm trying to run a timer for as long as the phone is asleep/idle. The timer will stop as soon as the phone is turned on.
<br>Here's the (relevant) code in main.java:

public void changeAppState(View view) {
        view = (Button) changeAppStateButton;
        Log.i("BUTTON", "Tapped!");
        if (isAppRunning) { //If the app is running, stop app
            isAppRunning = false;
            view.setBackgroundColor(getColor(R.color.colorPurple));
            view.setText("Start Reminder"); //There's an error here
            timer.cancel();
            Log.i("TIMER", "Timer interrupted");

        } else { //If the app is not running, start app
            //some code

            isAppRunning = true;
            view.setBackgroundColor(getColor(R.color.colorRed));
            view.setText("Stop Reminder"); //There's an error here

            //some more code
        }
    } 

This is the XML for the button:

    <Button
        android:id="@+id/changeAppStateButton"
        android:layout_width="0dp"
        android:layout_height="45dp"
        android:layout_marginStart="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginBottom="110dp"
        android:background="#9C27B0"
        android:fontFamily="@font/alegreya_sans_sc"
        android:onClick="changeAppState"
        android:text="Start Reminder"
        android:textAlignment="center"
        android:textColor="#FFFFFF"
        android:textSize="25sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent" />

Android Studio highlights both occurrences of setText() in the function. I don't see any error message.
Can someone tell me why setText() isn't working in the function? Let me know if you need more of the code.

Your reassigning of view doesn't change the type of the variable from View to Button as it gets re-cast automatically back to View.

Instead, you need to initialise a variable of type Button like so:

Button button = (Button) changeAppStateButton;

(or, as @Ahtisham pointed out, if you haven't already got a reference to the change app state button)

Button button = findViewById(R.id.changeAppStateButton);

Since this new variable is of type Button, you will be able to access its setText method.