Hi Yenctt,
You can find “nav-text” in header.php
<header id="header">
<?php if ( has_nav_menu('topbar') ): ?>
<nav class="nav-container group" id="nav-topbar">
<div class="nav-toggle"><i class="fa fa-bars"></i></div>
<div class="nav-text"><!-- put your mobile menu text here --></div>
<div class="nav-wrap container"><?php wp_nav_menu(array('theme_location'=>'topbar','menu_class'=>'nav container-inner group','container'=>'','menu_id' => '','fallback_cb'=> false)); ?></div>
Put your text in this line:
<div class="nav-text"><!-- put your mobile menu text here --></div>