Or open build/ios/archive/MyApp.xcarchive in Xcode.

    Click the Validate App button. If any issues are reported,
address them and produce another build. You can reuse the same
build ID until you upload an archive.

    After the archive has been successfully validated, click
Distribute App.

    
       Note:
  When you export your app at the end of Distribute App,
  Xcode will create a directory containing
  an IPA of your app and an ExportOptions.plist file.
  You can create new IPAs with the same options without launching
  Xcode by running
  flutter build ipa --export-options-plist=path/to/ExportOptions.plist.
  See xcodebuild -h for details about the keys in this property list.