It is not a big dial to refill cartridge itself. The problem is that the cartridge has a chip and after refilling toner,you will get a message on you printer "The cartridge is empty". Well, printer continues to print, but you won't be able to get received faxes printed.

There are three solutions:

The first item is not acceptable for the most small companies, at least in Russia for an obvious reason.

The  replacing a fuse method  demands some special  technical knowledge. It is easy to find what you need to replace (a fuse), but the problem how to do this:

But! As you understand manufacturer had to leave a backdoor for service centers. And it is easy to find this backdoor in google (using keywords from the left picture): 

Ok,  eventually, right solution (thanks ErikTheV):

When you will be typing this sequence, printer may not respond. Then just try with some pauses between MENU and numbers.Then "New Cartridge" appear, press "Enter". Type the sequence again.

Well, if it all fails you can always order a brand new cartridge. If you wonna see all that money go down the drain )
Читать все это на могучем. (Read post in Russian.)