What worked for me was to follow the instructions in this video: Resetting lever on cartridge There is a lever on the left hand side of the toner cartridge (left hand side - with you holding the cartridge as if you were going to insert it into the printer). It seems that lever has to be at the '12 o'clock' position to tell the printer that you have a new cartridge. The video showed the person removing 3 screws and then ensuring the lever was at the '12 o'clock' position. On my cartridge I had to do some wiggling to get the lever to move as it's gear assembly seemed to want it to only move down to the '4 o'clock position' and then stay there. Eventually I got it moved to 12 o'clock - and when I stuck the toner back into the printer - the 'toner end of life' message went away. I then removed the toner cartridge - as I wanted to try another cartridge that I had also reset the lever on. I found that lever had again moved to the 3 or 4 o'clock position - after printing just one test page so I am guessing it being at the 12 o'clock position tells the printer you have a new cartridge - and then it moves over to the regular position at 3 or 4 o'clock..
that's not a problem, the printer warns you when your toner is soon to end. Get a new cartridge to replace it when it is all used up. Tip: Toner warning comes on early, you can get more pages out by taking the drum out and shaking it carefully.
All electronic equipment with some intelligence in it, can be rewetted, by switching it off, removing the power cable and then connect and switch on again.
The machine should start the internal "program" from scratch.
In the manual it says you should leave it off for several minutes, if you want to initialise the copier again.