Hello @Prasanthi ,

Welcome to our community.

The WiFi password for your TP-Link Range Extender should be the same as your main router's WiFi password. The extender's network name typically appears as your router's name with "_EXT" added at the end.

Please check if you can properly connect the clients to the router, and check the Wi-Fi password.

Hello @VeroMakana ,

Thanks for contacting our community.

May I know the model number of your device? Please refer to How to find the model number of your TP-Link device 

Here are some suggestions that may help:
1. Hard reset the problematic extender: Use a pin to press and hold the reset button for 1-3 seconds until all lights flash.
2. Reconfigure it with a different WiFi name: Set it up again, but this time give it a unique WiFi name (different from both your router and your other extender). You can do this via the Tether app: How to configure Range Extender via Tether APP