prev / next button with slideshow

Hi Chris,
I’m back again with a last question (i hope so..)

Is there any keyword in the shortcode to show a prev/next button ?

Please see on my website: https://eexplore.fr

I decided to show testimonials one by one in a slideshow but there is no button to move forward or backward.

Here is the shortode

[strong slideshow nav="before,after" per_page="1" effect_for=".5" random title]
[client]
[field name="client_name" class="name"]
[field name="company_name" class="company"]
[/client]
[/strong]

nav=”before,after” is used but does not appear on screen

I’m probably wrong somewhere ??

Thanks again for your time.

All my best,
Phil

https://www.ads-software.com/plugins/strong-testimonials/