Hello, you can add both and control it with CSS:
<div class="custom-hide btn-cursor-pointer toggle-sidebar-left" data-toggle-class="sidebar-left-opened" data-target="html" data-fire-event="sidebar-left-opened">
<i class="fas fa-xmark" aria-label="Toggle sidebar"></i>
<i class="fas fa-bars" aria-label="Toggle sidebar"></i>
</div>
CSS:
.toggle-sidebar-left .fa-xmark {
display: none;
}
.toggle-sidebar-left .fa-bars {
display: block;
}
.sidebar-left-opened .toggle-sidebar-left .fa-xmark {
display: block;
}
.sidebar-left-opened .toggle-sidebar-left .fa-bars {
display: none;
}