please subscribe my channel - https://bit.ly/2Me2CfB

Sign in to YouTube Studio.
From the left Menu, select Customization. Basic info.
Under Channel URL, click Set a custom URL for your channel.
In the box, you'll see your custom URL. ...
Click PUBLISH, then Click CONFIRM to confirm your custom URL.

btw i cant edit my channel link bcoz i dont have my channel above than 100 subs
i have programming channel which will help you so please subscrie my channel - 
https://www.youtube.com/channel/UC7VZwb9aNdIr8_EoqdbOtIQ