Identity in ASP.Net Core 2.1< - Customize AccountController

ASP.NET Core 2.1 introduced new feature called Razor class libraries that lets you build views and pages as part of reusable library. ASP.NET Core Identity was moved to such RCL. You can override it in your project:

1. From Solution Explorer, right-click on the project > Add > New Scaffolded Item.
2. From the left pane of the Add Scaffold dialog, select Identity > ADD.
3. In the ADD Identity dialog, choose files you wish to override.
   1. Select layout if necessary
   2. Select or create Data context class.
4. Hit ADD.

For more information visit documentation.