To reset your router find the tiny reset button usually located at the back of the router.
While the router is on, use a pin or the end of a paper clip to press and hold the reset button. You will need to hold if for about 10 seconds.
Generally, you will want to wait for the lights to change on the router. Depending on the make and model of your router the lights may start out blinking and change to solid or they may start out solid and change to blinking.
When you let go of the reset button the router should be reset to the factory settings.