@nazia.naim 

Thanks for contacting us.

May I know what is the LED satus on your extender? Is it your first time to install it or extender just stops working?

You can try to reconfigure it. For the configuration of range extender, the wireless password is the key parameter. The range extender needs the correct wi-fi password to connect to your main wifi. If you are not sure about the wifi password of the main router, please refer to the FAQ below to check it via the existing wireless connection on your windows or mac computer:

How to find the wireless password on Windows 7/8/10 if my wireless network is already generated?
How to find the wireless password on a MAC if my wireless network is already generated?

After the wifi password is confirmed, please follow the steps to re-configure the range extender.
1.Reset it to prepare the setup:

How to hard reset TP-Link wireless access points, extenders to factory defaults
Note: Most LEDs should flash once when you reset it.
2.Re-configure it via Tether app:

How to configure Range Extender via Tether APP

Reconfiure it via web UI: 

How to configure my range extender via web GUI to extend an existing wireless network's coverage (new logo)?
More details please refer to our video if needed: https://youtu.be/oolmHBv7id8

If the above suggestions can't help you out, please share us with more details for the failure of the configuration, such as what's the prompt message when the configuration finished, the status of the LEDs in the device.