Because the minimal system requirements have changed after you updated your iPhone 7 plus to the newest version, the app may require an update. Apps must be supported by the current platform or iOS version of the phone in order to function properly. If you haven't set the app to auto-install updates, you'll have to manually install any pending updates. On your iPhone 7plus, follow these steps to check for and install pending app updates:

1. From the Home screen, tap the App Store icon.
2. Tap the Updates symbol in the bottom right corner of the App Store main screen. The screen then displays a list of apps that have outstanding updates.
3. From the list, select the Pandora music app, then hit the Update icon next to it. The Pandora app's pending update will then be installed.
4. If you see many app updates, you can update all of them at the same time. To do so, go to the upper right corner of the screen and tap the Update All button.