There are a few ways you might tackle this, but custom CSS is often a nice way to go, both because it’s “safer” than custom PHP and because you can easily tweak it to achieve a better fit. Plus, most themes make this really easy: simply navigate to Appearance ‣ Customize ‣ Additional CSS and add your code 🙂
/* Remove the titlebar area on forum archive pages */
.bbpress.forum-archive #page-titlebar {
display: none;
}
/* Retain some whitespace for consistency with other pages */
.bbpress.forum-archive #site-content {
margin-top: 75px;
}In this case, perhaps some rules like I’ve listed above could be a nice starting point?