How to programmatically trigger an event using Rx?

Question

.NET

Hello.
When we work with events directly, everything is simple

ListBox lb = new ListBox();
lb.SelectedValueChanged += LbOnSelectedValueChanged;
....
private void LbOnSelectedValueChanged(object sender, EventArgs eventArgs)
{
....
}

where LbOnSelectedValueChanged is called when the event fires, and can also be called directly.
Or you can use Rx, where there is a logic for working with an event

IObservable<EventArgs> selectedValueChanged = Observable.FromEventPattern<EventHandler, EventArgs>(
                            h => lb.SelectedValueChanged += h,
                            h => lb.SelectedValueChanged -= h).Select(x => x.EventArgs);

            selectedValueChanged.Delay(TimeSpan.FromSeconds(10)).Where(ts =>
            {                
                return IsCorrect();
            }).Subscribe(x =>
            {
                .....
            });

The question is how to call this event (with the given logic) programmatically?
(i.e. how to pull the subscriber and call OnNext for selectedValueChanged is not clear)