Best way, is to a 30-30-30 hard reset back to factory defaults.
1. With the router powered on, hold the reset button in for 30 seconds.
2. Continue to hold the reset button in and unplug the router, holding it in for another 30 seconds.
3. Plug the router back in, with the reset button still held, and continue to hold it in for another 30 seconds.
4. Once rebooted, do a quick soft reset.