Both destinations are served by Kochi (COK). Since there's no flight route between them, the best way to travel is by road.
Kottayam
Fly to Kochi (COK), then travel by road to Kottayam. Taxis, buses, and private cabs are available from the airport.
Kochi
Fly to Kochi Airport (COK), then travel by road to Kochi. Local transport options include taxis, auto-rickshaws, and state buses.