scoped_ServiceProvider.cs

public interface IService {}
public class ServiceA : IService {}
public class ServiceB : IService {}

// In your Startup.cs or ConfigureServices method
public void ConfigureServices(IServiceCollection services)
{
    services.AddScoped<IService, ServiceA>();
}

// Somewhere in your code where you want to switch the implementation
using (var scope = serviceProvider.CreateScope())
{
    var scopedServices = scope.ServiceProvider;
    var serviceDescriptor = new ServiceDescriptor(typeof(IService), typeof(ServiceB), ServiceLifetime.Scoped);
    ((ServiceCollection)scopedServices).Replace(serviceDescriptor);
    var service = scopedServices.GetRequiredService<IService>();
    // Now 'service' will be an instance of ServiceB
}