A. Ensure that your iPhone is running the latest version of iOS. Go to Settings > General > Software Update to check for updates. If an update is available, install it and then try reopening the app.
B. Delete the app from your iPhone and reinstall it. To do this, press and hold the app icon until it jiggles, tap the 'X' to delete it, then go to the App Store, search for the Friendly’s Restaurant app, and download it again.