For iOS
To Register your Flutter App to Firebase, you need to follow the following steps:
- Sign into Firebase using your Google account.
 - Create a Firebase project by clicking on Add project in the Firebase console and then entering a Project Name(e.g. flutterstarter).
 - To add an iOS app, click the icon to launch the setup workflow. Enter 
com.flutterstarter.appin the iOS bundle ID field. - Click Register App to continue.
 - Click Download GoogleService-Info.plist to obtain your Firebase iOS config file (
GoogleService-Info.plist). - Open XCode at 
ios/Runner/Runner.xcodeproj, move the file into the Runner/Runner directory of your Flutter app. 
Note: It’s important that you don’t simply drag this into the folder without going through Xcode, as this will not work.
- Add Flutter plugins in 
pubspec.yamlfile. 
- Run 
flutter packages getand you are good to go.