If I've started to put together a trip by reserving a hotel or car at the destination, then later want to add a flight, I can't see how to add a flight to the existing trip.  Is there a way to do this?  Or can I create two trips and merge them?

This also happens if I start with a flight, add hotel and rental car, then have to cancel the flight.  There's no way to add a flight back to the trip.

It doesn't prevent me from making reservations, it's just that the flight will be in a separate trip from everything else.

Thanks.