Copy and paste the code in functions.php of your current theme. Add your custom email template.

// Remove the container section in trackform
remove_filter( 'wp_new_user_notification_email', 'wpcfe_wp_new_user_notification_email', 10, 3 );
add_filter('wp_new_user_notification_email', 'custom_new_user_notification_email', 10, 3 );

function custom_new_user_notification_email( $wp_new_user_notification_email, $user, $blogname ){
    $user_login = stripslashes( $user->user_login );
    $user_email = stripslashes( $user->user_email );
    $headers    = array('Content-Type: text/html; charset=UTF-8');
    $headers[]  = __('From: ', 'wpcargo-frontend-manager' ) . get_bloginfo('name') .' <admin@no-reply.com>';
    $login_url  = wp_login_url();
    $message  = "<p>".__( 'Hi there,', 'wpcargo-frontend-manager' ) . "</p>";
    $message .= "<p>".sprintf( __( "Welcome to %s! Here's how to log in:", 'wpcargo-frontend-manager' ), get_option('blogname') ) . "</p>";

    //You can add custom message here...
 
    $wp_new_user_notification_email['subject'] = sprintf( '[%s] Your credentials.', $blogname );
    $wp_new_user_notification_email['headers'] = $headers;
    $wp_new_user_notification_email['message'] = $message;
 
    return $wp_new_user_notification_email;
}