Custom field group on page

I have what I hope is an easy question to answer, even if google has failed to provide me any solution.

Our main webmaster has set up custom field groups which we use with our custom post types for our webpage. Now I want to add a separate page, not using our custom post type, but a “pure” page and I want to use our custom field groups to on this page.

Is that at all possible?

When I tried to expand the screen options and to activate custom fields I do not have the option to add the already existing groups.

Hope you can help me out as I’m unable to contact the webmaster at the moment.

Edit: we are using WordPress 4.6.1