Currently I am using:

<?php wp_nav_menu( array('menu' => 'Second navigation', 'menu_id' => 'second_navigation', 'container' => false, 'menu_class' => 'nav', 'link_after' => '<span class="block sm__hidden"><img src="/images/icon_chevron.svg"></span> ') ); ?>

I get:

 <nav class="nav-primary">                    
    <ul id="second_navigation" class="nav">
        <li id="menu-item-2912" class="menu-item menu-item-type-custom menu-item-object-custom current-menu-ancestor current-menu-parent menu-item-has-children menu-item-2917">
        <a>Group
        <span class="block sm__hidden"><img src="/images/icon_chevron.svg">
        </span>
        </a>
            <ul class="sub-menu">
                <li id="menu-item-2672" class="menu-item menu-item-type-post_type menu-item-object-page current-menu-item page_item page-item-1156 current_page_item menu-item-2672">
                <a href="/one/" aria-current="page">One     
                <span class="block sm__hidden"><img src="/images/icon_chevron.svg">
                </span></a>
                </li>
                <li id="menu-item-2673" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-2673">
                <a href="/two/">Two     
                <span class="block sm__hidden"><img src="/images/icon_chevron.svg">
                </span></a>
                </li>
                <li id="menu-item-2674" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-2674">
                <a href="/three/">Three     
                <span class="block sm__hidden"><img src="/images/icon_chevron.svg">
                </span></a>
                </li>
            </ul>
        </li>
    </ul>   
</nav>

I want to achieve:

<nav class="nav-primary">                    
    <ul id="second_navigation" class="nav">
        <li id="menu-item-2912" class="menu-item menu-item-type-custom menu-item-object-custom current-menu-ancestor current-menu-parent menu-item-has-children menu-item-2917">
        <a>Group
        <span class="block sm__hidden"><img src="/images/icon_chevron.svg">
        </span>
        </a>
            <ul class="sub-menu">
                <li id="menu-item-2672" class="menu-item menu-item-type-post_type menu-item-object-page current-menu-item page_item page-item-1156 current_page_item menu-item-2672">
                <a href="/one/" aria-current="page">One</a>
                </li>
                <li id="menu-item-2673" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-2673">
                <a href="/two/">Two</a>
                </li>
                <li id="menu-item-2674" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-2674">
                <a href="/three/">Three</a>
                </li>
            </ul>
        </li>
    </ul>   
</nav>

I want the code <span class="block sm__hidden"><img src="/images/icon_chevron.svg"></span> to be only between <a>Group and </a>.

Please help me out to find out the solution.