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; } }