Download Unity Components that we have missed during the installation of Unity 3D

I install Unity 3D on Mac OS, due to slow internet, I only chosen the essential parts to download like Unity 3D, Standard Assets and so on…
Now I want to download the iOS and Android support, how to do that?

I simply re-run Unity’s Download Assistant (the installer) and selected only the additional packages I wanted to install. It installed it normally without removing the previous installed packages. Hope this works for you.
Best regards,