在Dashboard上为Wordpress管理面板创建表单

I am trying to create a dashboard widget using this wp_add_dashboard_widget hook. I have created a form with some input fields and submit button in it and that is properly appear in widget, but I'm not able to get and save that form fields using update_option function.

    function add_dashboard_widgets() {
    wp_add_dashboard_widget('dashboard_widget', 'Upload reports excel sheets', 'dashboard_widget_function');
    }
    add_action('wp_dashboard_setup', 'add_dashboard_widgets' );
    function dashboard_widget_function() { 
    $rto_status = get_option( 'rto_status', '' );
    ?>
    <form method="POST">
        <p><label for="rto_status">RTO Status</label>
        <input type="text" id="rto_status" class="jsAddReport" name="rto_status" value="<?php echo ($rto_status) ? $rto_status : ''; ?>" size="60" placeholder="click here to upload RTO Status" /></p>
<input type="submit" name="submit" value="update">
    </form>

In this case, I want to save the options on submit button.