Hi juansandro,
Each testimonial is wrapped in a div with a class called hms-testimonial-container.
Then each component is wrapped in an element usually a div. In the settings you can adjust the source between a blockquote and a div.
Once thing you could do is give all the child divs a padding of 5px in your themes style.css.
.hms-testimonial-container > div { padding-bottom:5px; }
Here is an example of what the testimonial container looks like:
<div class="hms-testimonial-container hms-testimonial-18 hms-testimonial-template-6">
<div class="testimonial">Testimonial content.</div>
<div class="url"><a rel="nofollow" href="https://google.com" target="_blank">https://google.com</a></div>
<div class="author">Test</div>
<div class="date"></div>
</div>