You created a Google Cloud Platform project with an App Engine application inside the project.

https://cloud.google.com/appengine/docs/flexible/managing-projects-apps-billing#:~:text=Each%20Cloud%20project%20can%20contain%20only%20a%20single%20App%20Engine%20application%2C%20and%20once%20created%20you%20cannot%20change%20the%20location%20of%20your%20App%20Engine%20application.

Two App engine can't be running on the same project: you can check this easy diagram for more info:https://cloud.google.com/appengine/docs/standard/an-overview-of-app-engine#components_of_an_application

And you can't change location after setting it for your app Engine.https://cloud.google.com/appengine/docs/standard/locations

App Engine is regional and you cannot change an apps region after you set it. Therefore, the only way to have an app run in another region is by creating a new project and targeting the app engine to run in the required region (asia-northeast1 in our case).

Ref: https://cloud.google.com/appengine/docs/locations