New theme/ I need full permission

I recently purchased a new wordpress theme and I can’t get one of the key features to work. At the top of my site, in between my menu and my blog feed I’m suppose to have a full page slider. Right now I’ve got an image but it isn’t a slider. According to the theme designer I should just be able to do the following steps to make it work:

“As of slider, you create it as usual: create your sliders using the Slider custom post, then go to Appearance – Customize – Content – Front page – Page slider and select the slider you created earlier, save and done.”

Once I click the “Front Page” option all it says is “Latest portfolio title” and underneath that it says “Enable section only if you have a title.” followed by a small type box.

When I reached out the theme designer for help they said:

“I don’t know, this is a 3rd party service or feature, you have to figure out why you don’t have full permission rights or features in your WP

in other words you have to find out why you don’t have our theme’s options under Customize – Content – Front page – Page slider”

Any clue how to fix this?
Thanks in advance!