// Nuget: Xamarin.Android.Arch.Work.Runtime

var r = PeriodicWorkRequest.Builder.From<MyWorker>(TimeSpan.FromSeconds(5))
    .SetConstraints(new Constraints.Builder()
        .SetRequiresCharging(true)
        .SetRequiredNetworkType(NetworkType.Unmetered)
        .Build())
    .Build();

WorkManager.Instance.Enqueue(r);

// ****************************************

public class MyWorker : Worker
{
    public MyWorker(Context context, WorkerParameters workerParameters)
        : base(context, workerParameters)
    {
    }

    public override Result DoWork()
    {
        Android.Util.Log.Debug("XAMARIN", "Work Request!");
        return new Result.Success();
    }
}