To add custom text under Menu items in Burger Menu, you can use this code to Code Injection > Footer.
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.0/jquery.min.js"></script>
<script>
$(document).ready(function(){
$('<div class="text-under-mobilemenu"><p>676 Old McLean Village Drive, #200 McLean, VA22101 USA</p><p><a href="tel:5713781782">5713781782</a></p></div>').insertAfter('.header-menu-nav-wrapper');
});
</script>
<style>
.text-under-mobilemenu {
margin-left: 5vw;
margin-right: 5vw;
padding-left: 4vw;
padding-right: 4vw;
text-align: left;
color: #fff;
}
.text-under-mobilemenu>p:first-child {
max-width: 250px;
}
</style>

Result
