To hide previous / next arrows on Slider layout, you can use following JS code:
// triggers when gallery is ready
document.addEventListener('galleryReady:covetPics', function(e) {
// prepare CSS styles to inject
const customStyles = document.createElement( 'style' )
customStyles.innerHTML = `
.swiper-button-next, .swiper-button-prev { display: none }
`
// get Covet gallery elements where you want to inject CSS (for eg. covet-pics-widget, covet-pics-popup, covet-pics-upload)
const widget = document.querySelector("covet-pics-widget");
// now inject CSS code into shadow DOM
widget.shadowRoot.appendChild(customStyles);
});