This is the React Native code for the IOS app that we have talked about. It uses a handy little thing called Expo to automatically sync your code to a simulation that can be running on your phone. It's truly brilliant. You will have to download the Expo app for iPhone or Android. See https://expo.io/.
To run it, just type npm install and npm start. Then scan the QR code that shows up in the terminal window from within the Expo app. Hopefully it will work.