The closest and most convenient International airport for you is to fly to New Delhi. If you are visiting India for the first time then it is better for you to take a flight to Domestic Airport Jollygrant Dehradun (city nearby), and from this domestic Airport, Rishikesh is a 45 min drive by car, so you save a hustle. If you request by email, The school will also help to arrange the Car/Cab and send a driver and he will drop you directly from the airport to the school without any stop.