Make sure the Cisco router is turned off and the power cord is plugged into both the router and the power source.
Look for the small factory reset button on the back of the router. Don't press it yet! Just make sure you can locate it.
To initiate a factory reset, you need to press and hold the power button and the factory reset button at the same time for at least 10 seconds.
After you initiate the factory reset, the router will take 5 - 10 minutes to boot. When the lights blink in repetitive patterns or stay solid, you'll know the router is back online.
Restart the router—when it boots again, the factory default settings will be restored.