Edit Navbar

Go to Appearance >> Menu

No “Menu” option? Enable by adding the following to functions.php

function mytheme_register_nav_menus() {
    register_nav_menus( array(
        'primary' => __( 'Primary Menu', 'your-text-domain' ),
        'footer' => __( 'Footer Menu', 'your-text-domain' )
    )); 
	}
	add_action( 'after_setup_theme', 'mytheme_register_nav_menus' );

Save the file, and it should be there under Appearance,

Display Menu on Theme

Add the following to functions.php

function wpb_custom_new_menu() {
  register_nav_menu('my-custom-menu',__( 'My Custom Menu' ));
}
add_action( 'init', 'wpb_custom_new_menu' );

Replace HTML static navbar to WordPress menu by adding this line to header.php

<?php wp_nav_menu( array( 'theme_location' => 'header-menu' ) ); ?>