@Vinothkumar2314 

May I know what is the model number of your range extender?

There are different passwords associated with the TP-Link range extenders. If you've forgotten any of them, consider the following scenarios: 
Scenario One: Forgot the login password to manage the extender.
    1. Try the default login password, which is often "admin".
    2. Perform a hard reset on the extender by pressing the reset button until the lights flash briefly. 
Scenario Two: Forgot the TP-Link ID password.
    1. Open the Tether app and select "Forget Password" on the login screen.
    2. Enter the email linked to your TP-Link ID and click "Reset Password," prompting a password reset email to be sent to you.
    3. Locate the email in your inbox, open it, and follow the steps to set a new password.
Scenario Three: Forgot the Wi-Fi password for the extender.
    1. Once set up, the extender's Wi-Fi password is the same as your router's.
    2. Open the Tether App, log into the extender under Devices, and tap Extended Network to view the Wi-Fi password. 
    3. Reach out to your router's support for the Wi-Fi password. 
    4. If the router's Wi-Fi password isn't working, hard reset the extender and follow the Tether app's instructions to set it up again.