Do 30-30-30 reset and then you can set your new username and password.
After 30-30-30 reset type 192.168.11.1 into your browser and you should be asked for your new login details.
To do a 30-30-30 reset you must push the reset button with your router powered on. Hold it for 30 seconds with the router powered on. STILL holding it, pull the power cord for 30 seconds. Still holding it, plug the power back into your router and continue to hold the reset button for 30 more seconds. You will have held the button for a full 90 seconds without releasing it.