Hi, 

If you forgot the administrator username to log in the tplink, the only way is to reset the router. Please find the reset button on the device, press it until all the lights flash once. After factory reset, you can log in with default username or create a new username to configure the tplink again.

If you have registered tplink cloud account and bound the router to it, then click "Forgot password" button when you log in to reset password.