Open project with Xcode (https://developer.apple.com/xcode/). Click .xcworkspace from project archive to open it.
Change the Bundle Identifier and Team Section
To make in-app purchases work, create them in Appstore and change shared secret and purchases IDs inside app.
Add Firebase to your project (https://firebase.google.com/docs/ios/setup)
Upload .json file to Firebase Database.
Launch project to test it.
Submit app to the AppStore (https://developer.apple.com/ios/submit/). Also re-skin the app before the AppStore submission.
Write me if you have any questions.