Simply visit Google’s Developer website here:
Configure a Button | YouTube Subscribe Button
| Google Developers
Then type in your Channel Name or ID in the box on the top right where it says: Your Channel Name or ID, and then choose the options presented below that by clicking on the drop-down selections there. They are Layout: select either default or full, Theme: select either default or dark, Subscriber count: default or hidden. That’s it, there will be a Preview under that will show how your subscribe button will look, and underneath that there will be a box that says CODE. Simply copy and paste the code that appears in that box where you want the Subscribe button to appear on your website.