Link. – Open the front cover and leave open while completing the following steps.
– Turn the printer off.
– Hold the ‘go’ button (or "start’ button) while turning the printer on. All panel lights should be on.
– Release the ‘go’ button (or "start’ button).
– Press the ‘go’ button (or "start’ button) 2 times.
– Pause. All panel lights should be on.
– Press the ‘go’ button (or "start’ button) 5 times.
The toner light should be off. (error may be flashing)
The paper light should be on or flashing.
– Close cover. The ready light should be the only light on.

Or use Bonjour Browser to find IP address and then http://10.0.1.22/printer/main.html then printer settings then un/pw user access then Replace Toner (continue). (Brother’s admin tool may also work.)