If you want to add an icon in your item in menu, default icon will be in top of your item, so if you ned to have it in left of your item, you need to add this code in custom.css from templates/name of theme/css/custom.css

.sp-megamenu-parent > li img {
display: inline;
height: auto;
max-width: 100%;
padding-bottom: 3px;
padding-right: 7px;
}

before

after fix: