@Subrata8777 

Hi,

If you've only lost the Wi-Fi password, but still know the admin password of your Archer C50, then just log into its management webpage (usually http://192.168.0.1 ) and get the Wi-Fi password from the "Wireless x GHz" -> "Wireless Security" menu.
In case your Archer C50 is an older version (V4 or older) and you have never configured any password, then you can try to log into the management webpage with username admin and password admin, which are the default values.

However, if you mean you have lost a customized admin password, then you will have to reset the C50 by pressing and holding the small button labelled "RESET". Note that doing this will reset all settings within the router.