The Manage iOS Code Signing Step in Bitrise allows for automatic code signing and exporting of Flutter iOS apps by managing provisioning profiles and certificates. To use this step, one must first upload the necessary code signing certificates to Bitrise, connect their Apple Developer Portal account, and then configure the workflow to include the Manage iOS Code Signing Step, Flutter Build Step, and Export iOS and tvOS Xcode Archive Step. The Manage iOS Code Signing Step downloads and installs certificates, generates and updates provisioning profiles, verifies and registers bundle IDs on the Apple Developer Site, and registers iOS devices with the developer site. The Flutter Build Step builds and signs a Flutter iOS app using the assets downloaded and installed in the previous step, while the Export iOS and tvOS Xcode Archive Step exports an .ipa file from an existing iOS .xcarchive file created by the Flutter Build Step. Once the workflow is configured, one can start a new build and view the output artifacts to verify successful code signing and exporting of the Flutter iOS app.