Slider enabled but not showing

I have installed the Sixteen theme and am enjoying it but cannot get the slider to show up on posts or pages. I have uploaded an image of the correct dimensions.

https://www.heartbeatsfitness.com

Most of my pages were created using Optimize Press and I was not expecting the slider to work on those pages but I have tried creating pages with the Sixteen theme and it still does not work.

I uploaded a Header image and that works in my blog posts, but still no slider.

Any help in easy to understand language is appreciated.