sdk-for-dart/docs/examples/project/delete-platform.md

import 'package:dart_appwrite/dart_appwrite.dart';

Client client = Client()
    .setEndpoint('https://<REGION>.cloud.appwrite.io/v1') // Your API Endpoint
    .setProject('<YOUR_PROJECT_ID>') // Your project ID
    .setKey('<YOUR_API_KEY>'); // Your secret API key

Project project = Project(client);

await project.deletePlatform(
    platformId: '<PLATFORM_ID>',
);