Im not very experienced on iMacs all my experience is on PC, anyway, I tried to reinstall my OS via the internet on my (Fusion Drive) as I suspected I had malware, anyway when I finished formatting the SSD and the HDD (in Mac Journaled) it only gave me the option to install the new OS on the SSD which is too small and not on the HDD - 1TB which is where I wanted to install. Why isn’t the HDD available as an available volume? Can anyone help?