its a landrover 90 2.5td

I recently had the engine in my land rover changed and the diesel mixture was set too high i was just wondering if there was any way to turn it down if yes then how????????

my land rover 90 smokes when it idles but dosent when i drive it. but it has just had a compleat engin overhall and all the piston rings done any ideas what it could be? its a 2.5 td 90 1989