Start by unplugging the power cable from the back of the Airport Extreme and locate the reset button.
Now, insert the pen, pin, or paperclip end into the reset button on the back.
When you hold the reset button, reconnect the power plug into make socket on the back of the Airport Extreme.
Keep the reset button depressed for about 6-7 seconds or until you see the light on the front of the Airport Extreme flash rapidly. It should be of amber color.
Now, wait for a minute for Airport Extreme to restart.