Yes! If you are registered for more than one event within the same event program (e.g. the same walk event in two different locations) you can access and fundraise for both events with the same app. Depending on the system the organization uses for collecting donations, the extra events should be automatically added to your application. You should see the different events for which you are registered in a drop-down menu at the top of the page or on the login page.
If you are not seeing all your registrations within the application, you should visit the Participant Center or HQ page for the event for which you are registered and click on the Boundless Fundraising™ installation links to make sure they are added properly. These links are typically displayed as a blue box with the words "Fundraise with Facebook" and will automatically install the app on the Facebook account that is logged into at that time.