Sort events on admin automatically by event-date

Hello, this is what I accomplish by now:
– register custom post type “myevents”
– create a custom field event-date (with plugin Advanced Custom Fields)
– create a custom column (in admin page for myevents) to show event-date and make that column sortable
Also, I have no problem displaying/showing events on page templates.

The thing I want to change is the myevents order on admin page.
So, on admin page for cpt myevents I can see the column with event dates ( also accomplish to show dates in my local format).
And that column IS SORTABLE WHEN I CLICK on it.

But when I enter that admin page for cpt myevents, all events are first sorted by the “published on” order – sorted by the date when they are published.

I would like to sort them from the beginning, the very moment I open the admin page, by their custom field event-date which is visible in the custom column I made.

For now I have to click on that column to sort them.

All the articles and tutorials helped me to make myevents and sortable custom column, but I don’t know how to accomplish so events are sorted
by event-date the first moment I open their admin page.

Here is the code (register cpt):

<?php
/*
Plugin Name: MyCPT
*/
add_action( 'init', 'my_cpt' );

function my_cpt() {

register_post_type( 'myevents', array(
  'labels' => array(
    'name' => 'My events',
    'singular_name' => 'My event',
	'add_new' => __('Dodaj Novu'),
	'add_new_item' => __('Dodaj Novu Najavu'),
    'edit_item' => __('Uredi Najavu'),
    'new_item' => __('Nova Najava'),
    'view_item' => __('Pregled Najave'),
   ),
  'description' => 'Najave.',
  'public' => true,
  'menu_position' => 20,
  'supports' => array( 'title', 'editor', 'custom-fields', 'thumbnail', 'excerpt' ),
  'taxonomies' => array( 'category', 'post_tag' )
));
}
?>

And here is the code from my functions.php (for sortable custom column), my custom field for event-date is called “datum_najave”:

<?php
// Register a new column in the admin Post area

add_filter('manage_edit-myevents_columns', 'my_dat_najave_column');
function my_dat_najave_column($columns) {
    $columns['datumnajave'] =__('Datum najave');
    return $columns;
}  

// add content

add_action( 'manage_myevents_posts_custom_column', 'my_dat_najave_column_content', 10, 2 );
function my_dat_najave_column_content( $column_name, $post_id ) {
    if ( 'datumnajave' != $column_name )
        return;
    //Get dates from post meta
    $datumnajave = get_post_meta($post_id, 'datum_najave', true);
    esc_html_e( date_i18n( 'd.m.Y.' , strtotime( $datumnajave ) ) );
}  

//  make the column sortable

add_filter( 'manage_edit-myevents_sortable_columns', 'my_sortable_datum_column' );
function my_sortable_datum_column( $columns ) {
    $columns['datumnajave'] = 'datum';  

    //To make a column 'un-sortable' remove it from the array
    //unset($columns['date']);  

    return $columns;
}  

add_action( 'pre_get_posts', 'my_datum_orderby' );
function my_datum_orderby( $query ) {
    if( ! is_admin() )
        return;  

    $orderby = $query->get( 'orderby');  

    if( 'datum' == $orderby ) {
        $query->set('meta_key','datum_najave');
        $query->set('orderby','meta_value_num');
    }
}  ?>

I don’t know what to add to make events sortable by default by “datum_najave” instead of their “published on” date.