Brother DCP-L3551CDW Multi-function Color Laser-how to empty\fill toner and reset counter?

[canon-do]

Hi all. This Brother model may have a different number outside New Zealand. Is there a generic thread about refilling toner cartridges on a similar model?
Thanks.

BTW: I'm getting the 'WT BOX FULL SOON' message but I haven't printed more than a few thousand sheets.