Added the Alexandre's updated code.

UI/app/src/main/java/com/example/capstone/Apps.java

@@ -0,0 +1,29 @@
+package com.example.capstone;
+
+import androidx.appcompat.app.AppCompatActivity;
+
+import android.content.Intent;
+import android.os.Bundle;
+import android.view.View;
+
+import com.google.firebase.auth.FirebaseAuth;
+
+public class Apps extends AppCompatActivity {
+    FirebaseAuth fAuth;
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_apps);
+        fAuth = FirebaseAuth.getInstance();
+    }
+
+    public void logout(View view){
+        fAuth.signOut();
+        startActivity(new Intent(getApplicationContext(), Login.class));
+        finish();
+    }
+
+    public void back(View view){
+        startActivity(new Intent(getApplicationContext(), homepage.class));
+    }
+}