@Sunchand 

Hi, do you mean login password of the web interface? It is usually admin in lower case, if it doesn't work, please reset the extender into default settings again by holding the reset button until all lights flashing once, then refer to this instruction to configure your range extender again carefully:

Via Tether App: https://www.tp-link.com/support/faq/1373/
Via Web interface: https://www.tp-link.com/support/faq/1400/

If there is still any problem, please share with me details of the problem and LED status on the extender.