Press and hold the Reset button on the back of the DSL-124 for 15 seconds while the power is on. Wait 2 minutes for the device to reboot.
: Updates may reset your router to factory defaults. Back up your ISP login credentials and wireless settings before starting. Step-by-Step Firmware Update Guide How do I upgrade the firmware on my router? | D-Link UK D-link Dsl-124 Firmware
If you care about security, treat the DSL-124 as a ticking time bomb if it faces the public internet. Use the official firmware only as a temporary bridge until you can install OpenWRT or replace the unit entirely with a modern VDSL2 router. Press and hold the Reset button on the