Insert banner ad on homepage

Hi,

My theme says that they cannot help me with this feature yet, but maybe there’s another way to accomplish this. There has to be.. but is there any way to insert a banner ad on the bottom of my homepage? Right under the post thumbnails, above the footer.

https://www.riverhillstraveler.com/wp-content/uploads/Screen-Shot-2017-09-04-at-1.40.44-PM.jpg

The page I need help with: [log in to see the link]