To add a 2-minute warning sound before breaks end in the Productivity Challenge Timer, follow these steps:

1. Check for the Latest Version: Ensure you are using the latest version of the Productivity Challenge Timer app. Look in the app store for updates. Keeping the app updated ensures you have access to the latest features and improvements.

2. Open the Settings: Launch the Productivity Challenge Timer app and navigate to the Settings menu. This is typically represented by a gear icon.

3. Locate Sound or Alert Settings: Within the Settings menu, search for Sound or Alerts options. These settings generally allow you to customize the sounds that play during productivity sessions and breaks.

4. Enable Break Warnings: Look for an option related to break or session alerts. If the feature to set a specific warning sound for breaks isn’t available by default, you may need to enable any general alert or sound settings associated with break notifications.

5. Set the Warning for 2 Minutes: If the app provides a timing feature for alerts, specify a 2-minute warning sound before break ends. This may be labeled under Session Duration, Break Duration, or similar.

6. Choose a Sound: Select an appropriate sound for the 2-minute warning. The app may offer various sound options, such as notifications or alarms, to choose from.

7. Save Settings: After configuring your preferences, ensure you save your settings. Look for a Save or Apply button, which confirms your adjustments.

8. Test It Out: After saving, begin a work session to see if the 2-minute warning functions as expected. Monitor the transition from the break and ensure the alert plays at the designated time.

If the app does not have a built-in option for a 2-minute warning sound specifically before breaks end, you might consider providing feedback to the app developers through the app store or official website to suggest adding this feature in future updates.

Note that the capabilities of features may vary based on the version of the app you are using. For further clarification on the app's functionality, refer to the app's official pages: Productivity Challenge Timer on the App Store - [learn more] or Productivity Challenge Timer on Google Play - [learn more].