Can I get some help please?

[Demonstr8]

Help adding subscribe button on mobile device

 

[Muzafir]

i also need to add button

 

[Nothin' But Gadgets]

Okay, I think what you are talking about is called "Branding". It is a watermark branding that appears in the lower lefthand corner of the video and people can click on it to subscribe. Here is how to add this.

Got to your Analytic page and click on "Customization" from the left menu. Then click on the "Branding" tab at the top under "Channel Customization". Follow the guide there to add a branding mark.