Hi, after a few hours, I finally figured this out.
To reset brother mfc-L3770CDW to factory defaults when we don't know the IP address and the menu is locked:
Hold a HOME button for few seconds, 4 fields appear, click last (empty one), next press *2864 on a touchscreen keyboard and MAINTENANCE should apper on the top left.
Next input 01, confirm question SELECT 01 with "Mono Start" button (on touchscreen), wait few seconds, then input 99 and then printer will reboot into factory defaults.
Info from here https://www.laserexpressinc.com/man...l3745cdw-l3750cdw-l3770cdw-service-manual.pdf
To reset brother mfc-L3770CDW to factory defaults when we don't know the IP address and the menu is locked:
Hold a HOME button for few seconds, 4 fields appear, click last (empty one), next press *2864 on a touchscreen keyboard and MAINTENANCE should apper on the top left.
Next input 01, confirm question SELECT 01 with "Mono Start" button (on touchscreen), wait few seconds, then input 99 and then printer will reboot into factory defaults.
Info from here https://www.laserexpressinc.com/man...l3745cdw-l3750cdw-l3770cdw-service-manual.pdf