I figured it out like this:
<?php
// Create and populate an object.
$user_record = new stdClass();

// Must be a valid primary key value.
$user_record->id = JFactory::getUser()->get('id');
$user_record->accept = '1';

// Update their details in the users table using id as the primary key.
$result = JFactory::getDbo()->updateObject('jos_jsn_users', $user_record, 'id');
?>

Hi,
sorry for late response, it was a weekend for us.

Alternately you can use our API, see at https://www.easy-profile.com/docs/38-jsnuser-object.html

Example Code:

require_once(JPATH_SITE.'/components/com_jsn/helpers/helper.php');

$user=JsnHelper::getUser();

$user-> accept ='1';

$user->save();