How do I set minSdk to 20?

I ran into an error here

FAILURE: Build failed with an exception.* Where:Build file 'C:\Users\Ayool\Downloads\src\instagram_flutter\googlemapsapi\gmaps_api\hope_google_maps_api\mapsgoogleapi\gmapsapi\android\app\build.gradle' line: 48* What went wrong:A problem occurred evaluating project ':app'.> Cannot get property '20' on null object* Try:> Run with --stacktrace option to get the stack trace.> Run with --info or --debug option to get more log output.

So I tried setting minSdk to 20

defaultConfig {        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).        applicationId "com.example.gmapsapi"        // You can update the following values to match your application needs.        // For more information, see: https://docs.flutter.dev/deployment/android#reviewing-the-gradle-build-configuration.        minSdk 20         targetSdk flutter.targetSdkVersion        versionCode flutterVersionCode.toInteger()        versionName flutterVersionName    }

But this error message pops up: "You don't have an extension for debugging Grade. Should we finda Gradle extension in the Marketplace?"