I assume this slider exists on this page only.
Open up page settings §, click on the gear icon of this page,
go all the way to the bottom to Custom Code > Footer Code, and paste this inside:
<script>
var Webflow = Webflow || [];
Webflow.push(function() {
var l = $('#myCustomSlider .w-slider-arrow-left');
var r = $('#myCustomSlider .w-slider-arrow-right');
$('#myCustomSlider')
.on('click', '.slider-left', function() {
l.trigger('tap');
})
.on('click', '.slider-right', function() {
r.trigger('tap');
});
});
</script>
Save and publish and view at http://koad.webflow.io