Land Rover Repair: land rover 99 check engine light, good shape, rest of the story

Question
I took my 99 disco in for the 90k mile service.. $900 later they tell me everything is in good shape.  My check engine light had been on when I took it in.. they said it was a "breather hose"  and the problem was resolved.  After I picked up my disco I drove about 20 miles and the check light is on again.  Can I reset this myself in any way?  it had just rolled over to 90k after I picked it up.. is that why it came on?  

Answer
They probably read a code indicating the engine was running lean, and saw the cracked breatehr hose and changed it without thinking that there may be more to the story.

I'm sure if they changed the breather hose it was bad; we change them all the time.

But that wasn't all your problem.  You're going to have to figure out the rest of the story. It's not a matter of "resetting the light" . . . you've got to fix the problem.