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