Register dependency injection.

Program.cs

public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args) 
                .ConfigureServices((hostContext, services) =>
                {
                    //Register dependency injection
                    services.AddSingleton<IBackupService, BackupService>();
                    services.AddScoped<HttpClient>();
                    services.AddHostedService<Worker>();
                  
                });
    }