Hi,
You can try this CSS.
/* Add margin to the left of 6th child (for centering) */
nav#generate-slideout-menu ul li:nth-child(6) {
margin-left: auto;
}
/* Add margin to the right of last child (for centering) */
nav#generate-slideout-menu ul li:last-child {
margin-right: auto;
}
/* for setting icon size */
.slideout-navigation.main-navigation .main-nav ul li.menu-item-float-right a .fas, .slideout-navigation.main-navigation .main-nav ul li.menu-item-float-right a .fab {
font-size: 25px;
}