Add these codes to the Custom CSS box
Desktop & Mobile
/* Desktop + Mobile */
button.product-item-gallery-carousel-control {
display: none !important;
}

Desktop Only
/* Desktop Only */
@media screen and (min-width:992px) {
button.product-item-gallery-carousel-control {
display: none !important;
}
}

Mobile Only
/* Mobile Only */
@media screen and (max-width:991px) {
button.product-item-gallery-carousel-control {
display: none !important;
}
}
