• For iOS platform follow all the steps which are mentioned on firebase console.
• For this you must have enrolled apple developer account.
• Register your application with updated bundle id.
• Configure push notification and download development and distribution certificates.
• Add those certificates to your system keychain with double click on that certificates.
• Generate .p12 certificates and add both the certificates on firebase console.
• Download GoogleService-Info.plist file.
• Drag and Drop that file on ios -> runner folder.

Register new identifier

Configure Push Notification on Developer Account

Add .p12 certificates to Firebase Console