The back to top button will always go to the top.
However, you could add an element into a Hook Element in the generate_after_footer
hook:
<a class="go-to-section smooth-scroll" href="#your-section">GO</a>
Then position it with some CSS:
.go-to-section {
display: block;
height: 50px;
line-height: 50px;
width: 50px;
text-align: center;
position: absolute;
right: 20px;
bottom: 20px;
background: #222;
color: #000;
}
Then just activate smooth scroll in Customize > General.