Do you mean Eynsham? If so, then at Heathrow you need to take the express train that takes you to Paddington Station. From this station every 30 minutes, trains leave for Oxford, on the way for 1 hour. Train arrives at the Oxford City Center, Railway Station. On foot or a couple of bus stops and you are at the Oxford City Center bus station, Frideswide Square. From there go the buses to Eynsham, on the way about 30 minutes