Here is the step by step procedure:
1. Open the front cover: Leave the cover open while you perform the following steps.
If you can't follow the above then try looking at this video: Brother HL-L3230CDW Toner Reset
2. Access the menu: On the control panel, press the Back and Cancel buttons simultaneously (or "Back" and "Go" depending on the exact sub-model).
3. From the menu: Immediately press the Back button again.
4. Select Toner: Use the down arrow button to scroll through the toner options:
K=Black, C=Cyan, M=Magenta, Y=Yellow.
TNR-HC = High Capacity TNR-STD = Standard Capacity.
5. Confirm Reset: Select the cartridge you want to reset and press OK.6. Accept: Press the up arrow button to select "Reset" or "Accepted".
7. Close cover: Once the screen says "Accepted," close the top cover. The printer will reset and display "Ready".
If you can't follow the above then try looking at this video: Brother HL-L3230CDW Toner Reset