Testimonial Slider adding nav buttons

Hi everyone,
i’m trying to add some navigation buttons (previous, next) to the testimontial slider but it doesn’t seem to work.

I put 2 icons with links under my testimonial element and i try to fetch click event on them (with jquery) to activate next/previous element.

here is my jquery code for next element :

$('#temoignages .av_font_icon:last-child a').on( "click", function() {

    var elementActif ="";
    elementActif = $('div#temoignages div.avia-slider-testimonials .active-slide');
    var elementSuiv = elementActif.next();
    resetTimer(elementActif);

     if (elementSuiv.length > 0) {
    		elementActif.removeClass("active-slide");
    		elementActif.css({
          		"opacity": "0",
          		"transform": "translateZ(0px)",
          		"transition": "none",
          		"-webkit-transition": "none",
          		"visibility": "hidden",
          		"z-index": 2
        	});
    		elementActif.next().addClass("active-slide");
    		elementActif.next().css({
          		"opacity": "1",
          		"transform": "translateZ(0px)",
          		"transition": "none",
          		"-webkit-transition": "none",
          		"visibility": "visible",
          		"z-index": 3
        	});
      }
	});

but in this exemple, jquery always return the first element of the slider as the “active-slide”.
So my code work to change from 1st to 2nd slide, but not nexts…
But In the devtools i can see that the active-slide is not on the first element.
So strange !

So my question is, is there an easier way to activate next/previons element for this slider ?

Thanks a lot for your help.