Hi codenamewilson
Template uses svg image for these arrows:
.acm-testimonial.style-1 .owl-carousel .owl-nav > button {
-webkit-mask-image: url("../images/icon-left.svg");
mask-image: url("../images/icon-left.svg");
-webkit-mask-size: 100% 100%;
mask-size: 100% 100%;
background-color: #2E2E2E;
margin-right: 1rem;
font-size: 0;
width: 35px;
height: 25px; }
.acm-testimonial.style-1 .owl-carousel .owl-nav > button.owl-next {
-webkit-mask-image: url("../images/icon-right.svg");
mask-image: url("../images/icon-right.svg"); }
Those images locate in: ROOT/templates/ja_alpha/images/ folder
You can change to your image and override CSS as you wish.