To add a new testimonial, search for the testimonials-images-list block and copy/paste a slide item.
<div class="testimonial-item"> <div class="item-header l-tal-c"> <div class="auth-img l-dis-ib"><img src="Image path" alt=""></div> <h4 class="auth-name t-fw-l">Testimonial author</h4> </div> <div class="item-testim js-item-testim">Main testimonial</div> </div>