[Koha] OPAC CUSTOMIZATION ON KOHA 21.11.12

Hello, I just installed koha 21.11.12 running on ubuntu 20.04. i want to customize the koha OPAC. on the news section, I can't see opacheader to position my header. i can only see Librarian and OPAC interfaces, Librarian Interface, OPAC and slip. How do i position my header now? Murphy Igbudu