You can add below code in you javascript file: /themes/alexa/assets/js/custom.js
$(document).on('click', '.scroll-box-arrows .material-icons', function(e) {
if ($(window).width() < 768) {
setTimeout(function() {
var imgSrc = $('.product-images li:first-child img').attr('data-image-large-src');
$('img.js-qv-product-cover').attr('src', imgSrc);
}, 700);
}
});
This will change large images also.