The steps required to configure driver and rider are the same. After one is done you will need to repeat the steps for the other one as well.

Bundle Identifier

Go to the ios folder and open the workspace file in Xcode. In the left panel select the Runner Project and here you can see something like the below picture. You will need to fill the Display Name and Bundle Identifier with the ones of your choice.
Now on the same page go to the "Signing & Capabilities" Tab. Here you will need to select the development team with your Apple developer account so Xcode would make necessary adjustments on your Apple Developer accounts such as Identifiers. It will also let you know if Bundle Identifier you have chosen is available or not. If available it automatically reserves it for you.


Now head over to the Firebase project and create respective projects for rider and driver with the bundle Identifiers you have assigned previously.
With Firebase projects being created you can use the download Google-Services.plist file and replace the ones in the ios folder with the downloaded one.
Go back to the Xcode workspace and open the newly replaced Google-Services.plist file. Here you have a row named REVERSE_CLIENT_ID. Copy this row's value and paste it into the Info.plist file under Url schemes->Firebase. Replace the previous API Key.
With this being done your apps are ready to compile.
You can use the below command to get the Xcode archive. Opening this file in Xcode will automatically take you through the release to Testflight steps.
flutter build ipa

APN Notification

For iOS to receive notifications, you need to set up APN with firebase. To do this first retrieve the APN Authentication key from your Apple Developer account (push notification enabled on it) and then go to the Firebase console and under the Cloud Messaging section upload the key and enter the Team ID/Key ID on the appropriate fields for your iOS apps. Keep in mind you need to do this for both rider and driver apps but you can use the same key for both of them.