It isn't too difficult to do, I found the manual here on the eevblog site. I'm on my phone at the moment so can't help too much with finding and linking manuals.
What sort of equipment of you have in the way of bench multimeters or handheld multi meters?
I find that every month or so one channel will creep upto 1mA or so, so I just current calibrate that channel and all is good until next time. It's dissapointing that it needs to be done, but where my unit is gets a lot of temperature variance, so I put it down to that.