Next Prev button not visible

Hello Guys,
I am using Testimonials widgets on my websites to show testimonials. Here on https://callanerd.help/referenzen/ on right sidebar but unfortunately I am not able to figure out next prev button over the same is there anyway to display next prev button to slide out the testimonials.

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