To add a new testimonial in slider copy/paste a slide item and fill it with your data.
<div class="owl-carousel testimonials-slider"> <!-- Slide item --> <div class="item"> <img src="image source" alt="" class="reviewer-img"> <h5 class="reviewer-name l-after">Author name</h5> <p class="reviewer-text">Testimonial content</p> </div> </div>