There is no real need to zero a grinder because were all good enough to dial in the grinder regardless of what number is showing. However, to zero a grinder, turn the burr carrier all the way until it wont turn anymore i.e. counter-clockwise. This is the point at which burr is touching burr (metal to metal). Knock it back a bit, this is your zero point.
For all mazzers, the grind is held in place by a patented tension springs. To get access to the burrs, you need to unwind the burr carrier all the way. (i.e. turn coarser or clockwise)
You may or may have trouble with the screws that hold the burrs in place. In case, an impact screwdriver is your best friend. About $35 to $40 from Bunnings in the tool shop.
Other than that, youre laughing....easy to service.