This article describes the steps required to configure the app for iOS, including updating app name and bundle id (package name).
You can either open ios folder in xcode manually, or you can open any file under ios folder in android studio and click Open iOS module in Xcode in top right corner.When in Xcode, click folder icon in top right (Show project navigator) and then select Runner. This will open settings panel for flutter project. If you have iPhone connected also make sure to select it at as target at the top.
In Xcode -> General tab, change bundle name to the display name of your app and identifier to unique ID for your app (usually same one as ID you registered on App Store Connect).Rest of the settings should be configured already by flutter, but you might need to also select your team under Signing & Capabilities menu.
With iOS configuration done, app is ready for building and release.