1. GitHub Releases or IntelliJ IDEs Plugin Marketplace DartMappable page download plugin
2. Open in the IDE Setting -> Plugins, right click setting icon ⚙️ -> Install Plugin from Disk... selected you download file.

Provide JSON to dart data classes conversion for use in Flutter and Dart projects.
Support multiple serialization schemes with json_serializable, dart_mappable, freezed.

Right click on package -> New -> Json To DartMappable　And Then you will know how to use.
After converting JSON to dart classes, will be automatically run 'flutter pub run build_runner build --delete-conflicting-outputs'.

If you haven't added the dependency, it will automatically execute the command to add it.

If you change the fields in the class, right click on package -> Flutter Command -> Flutter Run Build Runner, shortcut key is Alt + r.

Open in the IDE Setting -> Tools -> DartMappable Settings, selected dart_mappable.
Don't forget to set up dart_mappable into your project : https://pub.dev/packages/dart_mappable
Add into your pubspec.yaml

dependencies:
  dart_mappable: ^3.0.0  
dev_dependencies: 
  build_runner: ^2.1.0
  dart_mappable_builder: ^3.0.2

Or Run command in Terminal

flutter pub add dart_mappable
flutter pub add build_runner --dev
flutter pub add dart_mappable_builder --dev

Open in the IDE Setting -> Tools -> DartMappable Settings, selected json_serializable.
Don't forget to set up json_serializable into your project : https://pub.dev/packages/json_serializable
Add into your pubspec.yaml

dependencies:
  json_annotation: ^4.8.0
dev_dependencies:
  build_runner: ^2.3.3
  json_serializable: ^6.6.0

Or Run command in Terminal

flutter pub add json_annotation
flutter pub add build_runner --dev
flutter pub add json_serializable --dev

Open in the IDE Setting -> Tools -> DartMappable Settings, selected freezed.
Don't forget to set up freezed into your project : https://pub.dev/packages/freezed
Add into your pubspec.yaml

dependencies:
  freezed_annotation: ^2.4.1
dev_dependencies: 
  build_runner: ^2.1.0
  freezed: ^2.4.1

Or Run command in Terminal

flutter pub add freezed_annotation
flutter pub add --dev build_runner
flutter pub add --dev freezed
# if using freezed to generate fromJson/toJson, also add:
flutter pub add json_annotation
flutter pub add --dev json_serializable