Convert Bootstrap navbar to WordPress menu

You can replace the ul element inside the div of class collapse navbar-collapse with wp_nave_menu as follow example.

                <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
                    <?php wp_nav_menu(
                        array(
                            'theme_location' => 'primary',
                            'container' => false,
                            'menu_class' => 'nav navbar-nav navbar-right'))
                    ?>
                </div>

You need to use this https://github.com/twittem/wp-bootstrap-navwalker , add the nav walker file and follow the instructions. Here's a sample from a random site I made, I'm not adjusting it to your own site because you'll need to learn this for all your future WP developments. It's incredible easy, check it out:

    <div id="nav">
    <nav class="navbar navbar-default navbar-fixed-top" role="navigation">
      <div class="container">
        <!-- Brand and toggle get grouped for better mobile display -->
        <div class="navbar-header">
          <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">
            <span class="sr-only">Toggle navigation</span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
          </button>
          <a class="navbar-brand" href="<?php bloginfo('url'); ?>"><img class="logo" src="<?php bloginfo('template_directory'); ?>/images/logo.png" alt="" /></a>
        </div>


        <?php
        wp_nav_menu( array(
                'menu'              => 'primary',
                'depth'             => 2,
                'container'         => 'div',
                'container_class'   => 'navbar-collapse collapse',
                'menu_class'        => 'nav navbar-nav',
                'fallback_cb'       => 'wp_bootstrap_navwalker::fallback',
                'walker'            => new wp_bootstrap_navwalker())
            );
        ?>
      </div><!-- /.container-fluid -->
    </nav>
</div><!-- #nav -->

As you may have noticed, basically you have to replace what is after your code's

 <!-- Collect the nav links, forms, and other content for toggling -->

with

<?php
    wp_nav_menu( array(
            'menu'              => 'primary',
            'depth'             => 2,
            'container'         => 'div',
            'container_class'   => 'navbar-collapse collapse',
            'menu_class'        => 'nav navbar-nav',
            'fallback_cb'       => 'wp_bootstrap_navwalker::fallback',
            'walker'            => new wp_bootstrap_navwalker())
        );
    ?>

and voila

To fix the dropdown menu problem you should:

1. go to class-wp-bootstrap-navwalker.php file

2. look for $atts['data-toggle'] ="dropdown"; and replace it with $atts['data-bs-toggle'] ="dropdown";