To change the arrow icons in Divi Blog Extra slider layout, add the following CSS code in the Divi Theme option.

.et_pb_blog_extras .swiper-button-prev::after {
    content: "\e04d";
    font-family: 'ETmodules';
}
.et_pb_blog_extras .swiper-button-next::after {
    content: "\e04e";
    font-family: 'ETmodules';
}

Note: You can insert the icon code as per your need. To get the Divi icon code look here.