[Rx1 Wizard]

I am trying Kodi 18 on a xbox1. I am trying to control main menu items, but The skin settings menu is gone.

[Klojum]

Nothing has changed in Kodi 18 from 17 concerning skin settings.
Try renaming/removing guisettings.xml and restart Kodi.

[Hitcher]

Which skin?

[Karellen]

but The skin settings menu is gone.

If you are using the default Estuary skin, it has been removed.

It is now located in Interface>Skin>Configure skin...