I assume you are asking about having a user cp button right here like in this picture?
Here is how;
Enter the Admin CP
Go to Style Manager and select the style you want to add it on (If you have multiple styles, you must edit it for each).
Go to Edit Templates
Go to Navigation / Breadcrumb Templates
Go to the 'navbar' template
FIND:
Code:
{vb:raw template_hook.navbar_start}
UNDER, ADD:
Code:
<li><a href="usercp.php{vb:raw session.sessionurl_q}" rel="nofollow">User CP</a></li>
Good luck!