Canon MP390

1)Printer on, press Additional Functions, Scan, Copy, Scan
Now you should be in service mode from there for waste ink tank reset it is simalar to what has already been posted

2)Select Test mode which is like the last avalabe selection
3)Select #8 Printer Test, it will do something here like cleaning or something then it will come up with some other option this is where it gets a bit confusing cause now all it says is like 8-2 or 8-3 push the + or - button until it says 8-3 then hit the select button

The menu will now say EEPRON Clear
Select Ink count which is option (0) and press set

Then press Stop/Reset Followed by the power button and then wait for it to restart.