How do you register services in the ASP.NET Core DI container?

Use services AddSingleton<>  AddScoped<> or AddTransient<> in the ConfigureServices method of Startup.cs.

Use services.AddSingleton AddScoped or AddTransient in Startup cs or Program.cs.

Can you check this

https://www.c-sharpcorner.com/article/getting-started-with-dependency-injection-in-asp-net-core-using-c-sharp/