Error Execution failed for task

Question

i'm a beginner in Android and i'm trying different programs but this error still show up

':app:processDebugManifest' Manifest merger failed with multiple errors

how i can fix it

this is my code

---

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.nhn.test">


    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        tools:replace="android:icon,android:theme"
        >
        <activity android:name=".MainActivity" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="Main2Activity"
            android:label="@string/title_activity_main2"
            android:theme="@style/AppTheme.NoActionBar" >
        </activity>
        <activity android:name=".Main2Activity" >
        </activity>
    </application>
    <android:replace>"android:icon"</android:replace>
</manifest>

---

this is the first layout

    package com.example.nhn.test;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

public class MainActivity extends AppCompatActivity {
public void BtnNex(View view){
Intent int1= new Intent(this,Main2Activity.class);
    startActivity(int1);
}
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

---

this is the second had one button

package com.example.nhn.test;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

public class Main2Activity extends AppCompatActivity {
    public void BtnPrev(View view){
        Intent int2= new Intent(this,MainActivity.class);
        startActivity(int2);
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
    }
}