Hi LaLa, First of all see if your tour operator has a bus service to BERGAMO (because that's where Orio al Serio Airport is. Secondly try looking up the airport's website and see if there is any mention of 'Trasporti' - Italian for transport.

You will need to get to Bergamo railway station and can get a train there for Desenzano - you should look up Italian State Railways on a search engine. Good luck and have a great holiday.