Change application's starting activity

Yes, you use the AndroidManifest.xml file. You can actually even have more than one launcher activity specified in your application manifest. To make an activity seen on the launcher you add these attributes to your activity in the manifest:

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

Go to AndroidManifest.xml in the root folder of your project and change the Activity name which you want to execute first.

Example:

<activity android:name=".put your started activity name here"
          android:label="@string/app_name">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

If you are using Android Studio and you might have previously selected another Activity to launch.

Click on Run > Edit configuration and then make sure that Launch default Activity is selected.