It tells you how in Bentley, but basically you drive for X miles (I think its 250-500, hell I can't remember - I'll look tonight). Anyhow, drive the recommended mileage, pull the little rubber plug on the plastic cover, stick a socket (15mm or 17mm) on a ratshit with short extension in the hole, loosen the tensioner bolt a bit, turn the engine over a revolution or two, retorque the bolt, put the rubber plug back in an you are good to go.