If you can't find Themer layouts in the Builder menu, it's almost always due to one of two reasons:
You don't have the Beaver Themer plugin installed.
The Beaver Themer plugin is a premium plugin that requires the Page Builder plugin to work. After you install Beaver Themer, you'll automatically see a Themer layouts option in the Builder menu.
You don't have the Builder menu enabled. If you do have Beaver Themer installed but you can't find the Builder menu in the WordPress admin panel, see the Related Article about how to enable it.