@mamunfathim100 

Hello, detailed issue description including the TP-Link device model as well as its hardware version will help a lot in addressing the issue, so don't hesitate to provide as more details as you can.

If you mean you cannot find the wireless network of the extender after setup, did you create a different network name for it when you reconfigure the extender? If not, it may copy the wireless name of your main router. For example, if your existing Wi-Fi name is ABCD, after configuration, the possible extended network names may be ABCD, ABCD_EXT, ABCD_EXT_5G, or the one you create by yourself.

If you want to change the Wi-Fi name, please refer to the below FAQ see detailed instructions:
How to find or change the wireless settings of TP-Link Range Extender

May it help.