تغییر لانچ اکتیویتی

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme">
        <activity
            android:name=".ScrollingActivity"
            android:theme="@style/AppTheme.NoActionBar">

        </activity>

        <activity
            android:name=".MainActivity"
            android:theme="@style/AppTheme.NoActionBar">

***********************************
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
***********************************

        </activity>

    </application>
</manifest>