When I create an app with a flutter create command, the flutter logo is used as an application icon for both platforms.
flutter create
If I want to change the app icon,
I would suggest You to use this website Linked Below
App Icon Creator
Step-1: upload The Image,
Step-2: Make necessary Changes And Click on download(dont change the file name)
Step-3: Extract the Downloaded Zip File In the respective folder
android/app/src/main/res