Registrationsdoes not have a mobile app, but you can add it to your home screen on your phone!
Go to https://registrations.planningcenteronline.com/ in Chrome, and tap the menu in the upper right corner.
Tap Add to Home screen from the menu.
Rename the shortcut if you want, and then tap Add.
Touch and hold the icon to place it where you want, or tap Add Automatically.
Now you have a shortcut that you can use to easily access Registrations from your device!